diff --git a/.envrc b/.envrc
new file mode 100644
index 000000000..1d953f4bd
--- /dev/null
+++ b/.envrc
@@ -0,0 +1 @@
+use nix
diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
index 46581a5c6..c33f66d0a 100644
--- a/.rubocop_todo.yml
+++ b/.rubocop_todo.yml
@@ -1,6 +1,6 @@
 # This configuration was generated by
 # `rubocop --auto-gen-config --auto-gen-only-exclude --exclude-limit 1000 --no-auto-gen-timestamp`
-# using RuboCop version 1.6.1.
+# using RuboCop version 1.13.0.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
@@ -188,7 +188,7 @@ RSpec/DescribeClass:
     - 'spec/models/factory_spec.rb'
 
 # Offense count: 172
-# Configuration parameters: Max.
+# Configuration parameters: Max, CountAsOne.
 RSpec/ExampleLength:
   Exclude:
     - 'spec/controllers/admin_pages_controller_spec.rb'
@@ -425,6 +425,7 @@ Rake/MethodDefinitionInTask:
     - 'lib/tasks/db.rake'
 
 # Offense count: 138
+# Configuration parameters: AllowedConstants.
 Style/Documentation:
   Exclude:
     - 'app/controllers/admin_pages_controller.rb'
diff --git a/.ruby-version b/.ruby-version
index 37c2961c2..860487ca1 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-2.7.2
+2.7.1
diff --git a/.travis.yml b/.travis.yml
index aaecfdc05..0467ace6d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,6 @@
 language: ruby
 rvm:
-  - 2.7.2
+  - 2.7.1
 cache:
   bundler: true
   yarn: true
@@ -17,17 +17,17 @@ env:
 
 matrix:
   include:
-  - env: FORCE_POSTGRES=true
-    services:
-    - postgresql
-  - env: DO_NOT_FORCE_POSTGRES=true
+    - env: FORCE_POSTGRES=true
+      services:
+        - postgresql
+    - env: DO_NOT_FORCE_POSTGRES=true
 
 before_install:
   - env
   - nvm install 12
   - yarn install
   - google-chrome-stable --version
-  - 'echo ''gem: --no-document'' > ~/.gemrc'
+  - "echo 'gem: --no-document' > ~/.gemrc"
   - gem update --system
   - gem install bundler
   - bundle config set --local deployment 'true'
diff --git a/Gemfile b/Gemfile
index 7815d897b..c77eecbe0 100644
--- a/Gemfile
+++ b/Gemfile
@@ -2,7 +2,7 @@
 
 source 'https://rubygems.org'
 
-ruby '2.7.2'
+ruby '2.7.1'
 
 gem 'active_hash'
 # OPTIMIZE: and cache expensive computations for faster boot times. It's
@@ -32,7 +32,7 @@ gem 'pundit'
 gem 'rack-canonical-host'
 gem 'rack-cors'
 gem 'rack-mini-profiler', require: ['prepend_net_http_patch']
-gem 'rails', '~> 5.2.4.3'
+gem 'rails', '~> 5.2.5'
 gem 'sanitize'
 gem 'sassc-rails'
 gem 'simple_form'
diff --git a/Gemfile.lock b/Gemfile.lock
index b501eda1a..9974aa701 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,45 +1,45 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    actioncable (5.2.4.4)
-      actionpack (= 5.2.4.4)
+    actioncable (5.2.5)
+      actionpack (= 5.2.5)
       nio4r (~> 2.0)
       websocket-driver (>= 0.6.1)
-    actionmailer (5.2.4.4)
-      actionpack (= 5.2.4.4)
-      actionview (= 5.2.4.4)
-      activejob (= 5.2.4.4)
+    actionmailer (5.2.5)
+      actionpack (= 5.2.5)
+      actionview (= 5.2.5)
+      activejob (= 5.2.5)
       mail (~> 2.5, >= 2.5.4)
       rails-dom-testing (~> 2.0)
-    actionpack (5.2.4.4)
-      actionview (= 5.2.4.4)
-      activesupport (= 5.2.4.4)
+    actionpack (5.2.5)
+      actionview (= 5.2.5)
+      activesupport (= 5.2.5)
       rack (~> 2.0, >= 2.0.8)
       rack-test (>= 0.6.3)
       rails-dom-testing (~> 2.0)
       rails-html-sanitizer (~> 1.0, >= 1.0.2)
-    actionview (5.2.4.4)
-      activesupport (= 5.2.4.4)
+    actionview (5.2.5)
+      activesupport (= 5.2.5)
       builder (~> 3.1)
       erubi (~> 1.4)
       rails-dom-testing (~> 2.0)
       rails-html-sanitizer (~> 1.0, >= 1.0.3)
     active_hash (3.1.0)
       activesupport (>= 5.0.0)
-    activejob (5.2.4.4)
-      activesupport (= 5.2.4.4)
+    activejob (5.2.5)
+      activesupport (= 5.2.5)
       globalid (>= 0.3.6)
-    activemodel (5.2.4.4)
-      activesupport (= 5.2.4.4)
-    activerecord (5.2.4.4)
-      activemodel (= 5.2.4.4)
-      activesupport (= 5.2.4.4)
+    activemodel (5.2.5)
+      activesupport (= 5.2.5)
+    activerecord (5.2.5)
+      activemodel (= 5.2.5)
+      activesupport (= 5.2.5)
       arel (>= 9.0)
-    activestorage (5.2.4.4)
-      actionpack (= 5.2.4.4)
-      activerecord (= 5.2.4.4)
-      marcel (~> 0.3.1)
-    activesupport (5.2.4.4)
+    activestorage (5.2.5)
+      actionpack (= 5.2.5)
+      activerecord (= 5.2.5)
+      marcel (~> 1.0.0)
+    activesupport (5.2.5)
       concurrent-ruby (~> 1.0, >= 1.0.2)
       i18n (>= 0.7, < 2)
       minitest (~> 5.1)
@@ -51,10 +51,10 @@ GEM
       capybara (~> 3.13, < 4)
       websocket-driver (>= 0.6.5)
     arel (9.0.0)
-    ast (2.4.1)
+    ast (2.4.2)
     autoprefixer-rails (10.1.0.0)
       execjs
-    awesome_print (1.8.0)
+    awesome_print (1.9.2)
     backbone-on-rails (1.2.0.0)
       eco
       ejs
@@ -65,7 +65,7 @@ GEM
       coderay (>= 1.0.0)
       erubi (>= 1.0.0)
       rack (>= 0.9.0)
-    binding_of_caller (0.8.0)
+    binding_of_caller (1.0.0)
       debug_inspector (>= 0.0.1)
     bootsnap (1.5.1)
       msgpack (~> 1.0)
@@ -73,26 +73,25 @@ GEM
       autoprefixer-rails (>= 5.2.1)
       sassc (>= 2.0.0)
     builder (3.2.4)
-    bullet (6.1.2)
+    bullet (6.1.4)
       activesupport (>= 3.0.0)
       uniform_notifier (~> 1.11)
     byebug (11.1.3)
-    capybara (3.34.0)
+    capybara (3.35.3)
       addressable
       mini_mime (>= 0.1.3)
       nokogiri (~> 1.8)
       rack (>= 1.6.0)
       rack-test (>= 0.6.3)
-      regexp_parser (~> 1.5)
+      regexp_parser (>= 1.5, < 3.0)
       xpath (~> 3.2)
     capybara-screenshot (1.0.25)
       capybara (>= 1.0, < 4)
       launchy
     chrome_remote (0.3.0)
       websocket-driver (~> 0.6)
-    codecov (0.2.12)
-      json
-      simplecov
+    codecov (0.5.2)
+      simplecov (>= 0.15, < 0.22)
     coderay (1.1.3)
     coffee-rails (5.0.0)
       coffee-script (>= 2.2.0)
@@ -101,11 +100,17 @@ GEM
       coffee-script-source
       execjs
     coffee-script-source (1.12.2)
-    concurrent-ruby (1.1.7)
-    crack (0.4.4)
+    concurrent-ruby (1.1.8)
+    crack (0.4.5)
+      rexml
     crass (1.0.6)
-    database_cleaner (1.8.5)
-    debug_inspector (0.0.3)
+    database_cleaner (2.0.1)
+      database_cleaner-active_record (~> 2.0.0)
+    database_cleaner-active_record (2.0.0)
+      activerecord (>= 5.a)
+      database_cleaner-core (~> 2.0.0)
+    database_cleaner-core (2.0.1)
+    debug_inspector (1.1.0)
     devise (4.7.3)
       bcrypt (~> 3.0)
       orm_adapter (~> 0.1)
@@ -113,7 +118,7 @@ GEM
       responders
       warden (~> 1.2.3)
     diff-lcs (1.4.4)
-    docile (1.3.2)
+    docile (1.3.5)
     dotenv (2.7.6)
     dotenv-rails (2.7.6)
       dotenv (= 2.7.6)
@@ -131,12 +136,12 @@ GEM
     factory_bot_rails (6.1.0)
       factory_bot (~> 6.1.0)
       railties (>= 5.0.0)
-    faker (2.15.1)
+    faker (2.17.0)
       i18n (>= 1.6, < 2)
     faraday (1.1.0)
       multipart-post (>= 1.2, < 3)
       ruby2_keywords
-    ffi (1.13.1)
+    ffi (1.15.0)
     font-awesome-rails (4.7.0.5)
       railties (>= 3.2, < 6.1)
     geocoder (1.6.4)
@@ -149,17 +154,17 @@ GEM
       tilt (>= 1.2)
     hashdiff (1.0.1)
     hashie (4.1.0)
-    i18n (1.8.5)
+    i18n (1.8.10)
       concurrent-ruby (~> 1.0)
     icalendar (2.7.0)
       ice_cube (~> 0.16)
     ice_cube (0.16.3)
-    jasmine (3.6.0)
-      jasmine-core (~> 3.6.0)
+    jasmine (3.7.0)
+      jasmine-core (~> 3.7.0)
       phantomjs
       rack (>= 1.2.1)
       rake
-    jasmine-core (3.6.0)
+    jasmine-core (3.7.1)
     jasmine-jquery-rails (2.0.3)
     jquery-rails (4.4.0)
       rails-dom-testing (>= 1, < 3)
@@ -167,26 +172,23 @@ GEM
       thor (>= 0.14, < 2.0)
     jquery-ui-rails (6.0.1)
       railties (>= 3.2.16)
-    json (2.3.1)
     jwt (2.2.2)
     kdtree (0.4)
     launchy (2.5.0)
       addressable (~> 2.7)
-    listen (3.3.3)
+    listen (3.5.1)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
-    loofah (2.8.0)
+    loofah (2.9.1)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
     mail (2.7.1)
       mini_mime (>= 0.1.1)
-    marcel (0.3.3)
-      mimemagic (~> 0.3.2)
+    marcel (1.0.1)
     method_source (1.0.0)
-    mimemagic (0.3.5)
-    mini_mime (1.0.2)
-    mini_portile2 (2.4.0)
-    minitest (5.14.2)
+    mini_mime (1.1.0)
+    mini_portile2 (2.5.1)
+    minitest (5.14.4)
     msgpack (1.3.3)
     multi_json (1.15.0)
     multi_xml (0.6.0)
@@ -197,12 +199,13 @@ GEM
       require_all
     nested_form (0.3.2)
     newrelic_rpm (6.14.0)
-    nio4r (2.5.4)
-    nokogiri (1.10.10)
-      mini_portile2 (~> 2.4.0)
+    nio4r (2.5.7)
+    nokogiri (1.11.3)
+      mini_portile2 (~> 2.5.0)
+      racc (~> 1.4)
     nokogumbo (2.0.4)
       nokogiri (~> 1.8, >= 1.8.4)
-    oauth (0.5.4)
+    oauth (0.5.6)
     oauth2 (1.4.4)
       faraday (>= 0.8, < 2.0)
       jwt (>= 1.0, < 3.0)
@@ -240,13 +243,13 @@ GEM
       rack
     orm_adapter (0.5.0)
     parallel (1.20.1)
-    parallel_tests (3.4.0)
+    parallel_tests (3.7.0)
       parallel
-    parser (2.7.2.0)
+    parser (3.0.1.1)
       ast (~> 2.4.1)
     pg (1.2.3)
     phantomjs (2.1.1.0)
-    pry (0.13.1)
+    pry (0.14.1)
       coderay (~> 1.1)
       method_source (~> 1.0)
     public_suffix (4.0.6)
@@ -254,6 +257,7 @@ GEM
       nio4r (~> 2.0)
     pundit (2.1.0)
       activesupport (>= 3.0.0)
+    racc (1.5.2)
     rack (2.2.3)
     rack-canonical-host (1.0.0)
       addressable (> 0, < 3)
@@ -265,18 +269,18 @@ GEM
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
     rack-timeout (0.6.0)
-    rails (5.2.4.4)
-      actioncable (= 5.2.4.4)
-      actionmailer (= 5.2.4.4)
-      actionpack (= 5.2.4.4)
-      actionview (= 5.2.4.4)
-      activejob (= 5.2.4.4)
-      activemodel (= 5.2.4.4)
-      activerecord (= 5.2.4.4)
-      activestorage (= 5.2.4.4)
-      activesupport (= 5.2.4.4)
+    rails (5.2.5)
+      actioncable (= 5.2.5)
+      actionmailer (= 5.2.5)
+      actionpack (= 5.2.5)
+      actionview (= 5.2.5)
+      activejob (= 5.2.5)
+      activemodel (= 5.2.5)
+      activerecord (= 5.2.5)
+      activestorage (= 5.2.5)
+      activesupport (= 5.2.5)
       bundler (>= 1.3.0)
-      railties (= 5.2.4.4)
+      railties (= 5.2.5)
       sprockets-rails (>= 2.0.0)
     rails-controller-testing (1.0.5)
       actionpack (>= 5.0.1.rc1)
@@ -287,55 +291,55 @@ GEM
       nokogiri (>= 1.6)
     rails-html-sanitizer (1.3.0)
       loofah (~> 2.3)
-    railties (5.2.4.4)
-      actionpack (= 5.2.4.4)
-      activesupport (= 5.2.4.4)
+    railties (5.2.5)
+      actionpack (= 5.2.5)
+      activesupport (= 5.2.5)
       method_source
       rake (>= 0.8.7)
       thor (>= 0.19.0, < 2.0)
     rainbow (3.0.0)
-    rake (13.0.1)
+    rake (13.0.3)
     rb-fsevent (0.10.4)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    regexp_parser (1.8.2)
+    regexp_parser (2.1.1)
     require_all (3.0.0)
     responders (3.0.1)
       actionpack (>= 5.0)
       railties (>= 5.0)
-    rexml (3.2.4)
+    rexml (3.2.5)
     rspec-collection_matchers (1.2.0)
       rspec-expectations (>= 2.99.0.beta1)
-    rspec-core (3.10.0)
+    rspec-core (3.10.1)
       rspec-support (~> 3.10.0)
-    rspec-expectations (3.10.0)
+    rspec-expectations (3.10.1)
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.10.0)
-    rspec-mocks (3.10.0)
+    rspec-mocks (3.10.2)
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.10.0)
-    rspec-rails (4.0.1)
-      actionpack (>= 4.2)
-      activesupport (>= 4.2)
-      railties (>= 4.2)
-      rspec-core (~> 3.9)
-      rspec-expectations (~> 3.9)
-      rspec-mocks (~> 3.9)
-      rspec-support (~> 3.9)
-    rspec-support (3.10.0)
-    rubocop (1.6.1)
+    rspec-rails (5.0.1)
+      actionpack (>= 5.2)
+      activesupport (>= 5.2)
+      railties (>= 5.2)
+      rspec-core (~> 3.10)
+      rspec-expectations (~> 3.10)
+      rspec-mocks (~> 3.10)
+      rspec-support (~> 3.10)
+    rspec-support (3.10.2)
+    rubocop (1.13.0)
       parallel (~> 1.10)
-      parser (>= 2.7.1.5)
+      parser (>= 3.0.0.0)
       rainbow (>= 2.2.2, < 4.0)
       regexp_parser (>= 1.8, < 3.0)
       rexml
       rubocop-ast (>= 1.2.0, < 2.0)
       ruby-progressbar (~> 1.7)
-      unicode-display_width (>= 1.4.0, < 2.0)
-    rubocop-ast (1.3.0)
-      parser (>= 2.7.1.5)
-    rubocop-performance (1.9.1)
-      rubocop (>= 0.90.0, < 2.0)
+      unicode-display_width (>= 1.4.0, < 3.0)
+    rubocop-ast (1.5.0)
+      parser (>= 3.0.1.1)
+    rubocop-performance (1.11.1)
+      rubocop (>= 1.7.0, < 2.0)
       rubocop-ast (>= 0.4.0)
     rubocop-rails (2.9.1)
       activesupport (>= 4.2.0)
@@ -343,12 +347,12 @@ GEM
       rubocop (>= 0.90.0, < 2.0)
     rubocop-rake (0.5.1)
       rubocop
-    rubocop-rspec (2.1.0)
+    rubocop-rspec (2.3.0)
       rubocop (~> 1.0)
       rubocop-ast (>= 1.1.0)
     rubocop-thread_safety (0.4.2)
       rubocop (>= 0.53.0)
-    ruby-progressbar (1.10.1)
+    ruby-progressbar (1.11.0)
     ruby2_keywords (0.0.2)
     sanitize (5.2.1)
       crass (~> 1.0.2)
@@ -364,17 +368,17 @@ GEM
       tilt
     sentry-raven (3.1.1)
       faraday (>= 1.0)
-    shoulda-matchers (4.4.1)
+    shoulda-matchers (4.5.1)
       activesupport (>= 4.2.0)
     simple_form (5.0.3)
       actionpack (>= 5.0)
       activemodel (>= 5.0)
-    simplecov (0.20.0)
+    simplecov (0.21.2)
       docile (~> 1.1)
       simplecov-html (~> 0.11)
       simplecov_json_formatter (~> 0.1)
     simplecov-html (0.12.3)
-    simplecov_json_formatter (0.1.2)
+    simplecov_json_formatter (0.1.3)
     spring (2.1.1)
     spring-commands-rspec (1.0.4)
       spring (>= 0.9.1)
@@ -386,18 +390,18 @@ GEM
       activesupport (>= 4.0)
       sprockets (>= 3.0.0)
     sqlite3 (1.4.2)
-    thor (1.0.1)
+    thor (1.1.0)
     thread_safe (0.3.6)
     tilt (2.0.10)
-    tzinfo (1.2.8)
+    tzinfo (1.2.9)
       thread_safe (~> 0.1)
     uglifier (4.2.0)
       execjs (>= 0.3.0, < 3)
-    unicode-display_width (1.7.0)
-    uniform_notifier (1.13.0)
+    unicode-display_width (2.0.0)
+    uniform_notifier (1.14.2)
     warden (1.2.9)
       rack (>= 2.0.9)
-    webmock (3.11.0)
+    webmock (3.12.2)
       addressable (>= 2.3.6)
       crack (>= 0.3.2)
       hashdiff (>= 0.4.0, < 2.0.0)
@@ -461,7 +465,7 @@ DEPENDENCIES
   rack-cors
   rack-mini-profiler
   rack-timeout
-  rails (~> 5.2.4.3)
+  rails (~> 5.2.5)
   rails-controller-testing
   rake
   rb-fsevent
@@ -487,7 +491,7 @@ DEPENDENCIES
   webmock
 
 RUBY VERSION
-   ruby 2.7.2p137
+   ruby 2.7.1p83
 
 BUNDLED WITH
    2.1.4
diff --git a/README.markdown b/README.markdown
index 91cdd42e1..7fa4ecde0 100644
--- a/README.markdown
+++ b/README.markdown
@@ -1,5 +1,5 @@
 # Bridge Troll
- 
+
 [![Build Status](https://travis-ci.com/railsbridge/bridge_troll.svg?branch=master)](https://travis-ci.com/railsbridge/bridge_troll)
 [![codecov](https://codecov.io/gh/railsbridge/bridge_troll/branch/master/graph/badge.svg)](https://codecov.io/gh/railsbridge/bridge_troll)
 
@@ -14,20 +14,23 @@ Prospective organizers and attendees can sign up right now at [www.bridgetroll.o
 New? Keep reading this, and then read the [contributor guidelines](CONTRIBUTING.md).
 
 ### Where is it?
-* The real live production application lives at [bridgetroll.herokuapp.com](http://bridgetroll.herokuapp.com/) or [www.bridgetroll.org](http://www.bridgetroll.org/)
-* The staging server lives at [bridgetroll-staging.herokuapp.com](http://bridgetroll-staging.herokuapp.com/)
-* The continuous integration server is at [travis-ci.org/railsbridge/bridge_troll](http://travis-ci.org/railsbridge/bridge_troll)
+
+- The real live production application lives at [bridgetroll.herokuapp.com](http://bridgetroll.herokuapp.com/) or [www.bridgetroll.org](http://www.bridgetroll.org/)
+- The staging server lives at [bridgetroll-staging.herokuapp.com](http://bridgetroll-staging.herokuapp.com/)
+- The continuous integration server is at [travis-ci.org/railsbridge/bridge_troll](http://travis-ci.org/railsbridge/bridge_troll)
 
 For details on how production and staging are setup, see the [deployment docs](doc/deploy.md).
 
 ### Features & Bugs
-* We use [GitHub Issues](https://github.com/railsbridge/bridge_troll/issues?state=open) for tracking bugs and features.
- * Issues marked as [Help Wanted](https://github.com/railsbridge/bridge_troll/issues?q=is%3Aissue+is%3Aopen+label%3A%22Help+Wanted%22) are ready to go, so pick one up!
- * Bugs are, naturally, [marked as bugs](https://github.com/railsbridge/bridge_troll/labels/bug).
- * Issues marked with the [Discussion label](https://github.com/railsbridge/bridge_troll/labels/Discussion) are currently being refined. If you're interested in working on one, comment and ask what needs to be finalized before it's ready to be worked on.
- * We also mark issues as [beginner friendly](https://github.com/railsbridge/bridge_troll/labels/Beginner%20Friendly), so if you're new to Rails, check those out.
+
+- We use [GitHub Issues](https://github.com/railsbridge/bridge_troll/issues?state=open) for tracking bugs and features.
+- Issues marked as [Help Wanted](https://github.com/railsbridge/bridge_troll/issues?q=is%3Aissue+is%3Aopen+label%3A%22Help+Wanted%22) are ready to go, so pick one up!
+- Bugs are, naturally, [marked as bugs](https://github.com/railsbridge/bridge_troll/labels/bug).
+- Issues marked with the [Discussion label](https://github.com/railsbridge/bridge_troll/labels/Discussion) are currently being refined. If you're interested in working on one, comment and ask what needs to be finalized before it's ready to be worked on.
+- We also mark issues as [beginner friendly](https://github.com/railsbridge/bridge_troll/labels/Beginner%20Friendly), so if you're new to Rails, check those out.
 
 ### Want to help out?
+
 Join the [google group](https://groups.google.com/forum/?fromgroups#!forum/bridge-troll) and send a quick note introducing yourself.
 
 Then, have a look at our [GitHub Issues](https://github.com/railsbridge/bridge_troll/issues?state=open). Pick a feature to work on, fork the project, code some code, and send a [really good pull request](http://railsbridge.github.com/bridge_troll/). Not sure what to do? Ask the [google group](https://groups.google.com/forum/?fromgroups#!forum/bridge-troll) for advice!
@@ -36,25 +39,28 @@ Curious about the longer-term? We have something of a roadmap [here](https://git
 
 ## Setting up for your local development environment
 
-You'll need a version manager for Ruby.  A version manager is a command-line tool which allows you to easily install, manage, and work with multiple ruby environments. We recommend [rvm](http://rvm.io), but [rbenv](https://github.com/sstephenson/rbenv) will work.
+You'll need a version manager for Ruby. A version manager is a command-line tool which allows you to easily install, manage, and work with multiple ruby environments. We recommend [rvm](http://rvm.io), but [rbenv](https://github.com/sstephenson/rbenv) will work.
 
 ### Quickstart
 
-We're using a fork & pull model (see [Fork A Repo](https://help.github.com/articles/fork-a-repo) for an example), so fork this repo then clone the *forked* repo.
-(Note: change *username* below to be *your* repo.)
+We're using a fork & pull model (see [Fork A Repo](https://help.github.com/articles/fork-a-repo) for an example), so fork this repo then clone the _forked_ repo.
+(Note: change _username_ below to be _your_ repo.)
+
 ```
 git clone https://github.com/username/bridge_troll.git
 cd bridge_troll
 ```
 
-Make sure you have the correct version of ruby before installing the gems for this repo. If you are using rvm, run: `rvm install 2.7.2`. For rbenv, run: `rbenv install 2.7.2`.
+Make sure you have the correct version of ruby before installing the gems for this repo. If you are using rvm, run: `rvm install 2.7.1`. For rbenv, run: `rbenv install 2.7.1`.
 
 Finish setting up your environment
+
 ```
 bin/setup
 ```
 
 To verify your environment is set up correctly, run the server
+
 ```
 rails s
 ```
@@ -62,8 +68,9 @@ rails s
 Go to http://localhost:3000/ and verify your success! You can play with the app locally to become more familiar with it.
 
 Pro-tip: Confirming Users Locally
-* outgoing emails are logged, so if you scroll back in your terminal window, you can see the contents of the confirmation email and copy/paste the confirmation link into your browser
-* or create a valid user for most recent signup, run `rails console`: `User.last.confirm!`
+
+- outgoing emails are logged, so if you scroll back in your terminal window, you can see the contents of the confirmation email and copy/paste the confirmation link into your browser
+- or create a valid user for most recent signup, run `rails console`: `User.last.confirm!`
 
 ### Running tests
 
@@ -98,18 +105,21 @@ All the created users have easyish-to-remember logins, so a great way to test ou
 Doing `rake db:seed` again will destroy all those sample persons and create the event again. The exact details of what is created can be found in `seed_event.rb`.
 
 #### Anonymizing Data
+
 You can replace sensitive personal information about events and participants from the data with a Rake task. Note that it will not run if your Rails environment is set to `production`.
-````
+
+```
 rake db:anonymize
-````
+```
 
 Restore the original data to your database with
-````
-rake db:restore
-````
 
+```
+rake db:restore
+```
 
 ### Styling Guidelines
+
 We have created a living style guide to keep track of HTML components and their styling across the site. See it at http://localhost:3000/style_guide.
 
 We're still working on adding every element to the page, so if you see missing components, add it to the erb template ([style_guide.html.erb](app/views/static_pages/style_guide.html.erb))
@@ -126,15 +136,15 @@ You can see rendered versions of all emails the application can send at http://l
 
 #### Mailcatcher
 
-  To receive/develop emails locally, install the MailCatcher gem at http://mailcatcher.me. The process is as follows:
+To receive/develop emails locally, install the MailCatcher gem at http://mailcatcher.me. The process is as follows:
 
-  1. `gem install mailcatcher` -- installs MailCatcher in your current gemset
-  1. `mailcatcher` -- start the MailCatcher server if it isn't running already
-  1. Visit http://localhost:1080/ in your web browser. This is your MailCatcher mailbox, where mails will appear.
-  1. Do something in your local Bridge Troll app that would send a mail, like signing up for a new account.
-  1. You should see the mail that Rails sent in the MailCatcher window. Woo!
+1. `gem install mailcatcher` -- installs MailCatcher in your current gemset
+1. `mailcatcher` -- start the MailCatcher server if it isn't running already
+1. Visit http://localhost:1080/ in your web browser. This is your MailCatcher mailbox, where mails will appear.
+1. Do something in your local Bridge Troll app that would send a mail, like signing up for a new account.
+1. You should see the mail that Rails sent in the MailCatcher window. Woo!
 
-  Note that MailCatcher just makes it easy to see the HTML output of your mails: it doesn't guarantee that the way the mail looks like in MailCatcher is how it will look in Gmail or Outlook. Beware!
+Note that MailCatcher just makes it easy to see the HTML output of your mails: it doesn't guarantee that the way the mail looks like in MailCatcher is how it will look in Gmail or Outlook. Beware!
 
 ### Working with external services
 
@@ -158,12 +168,12 @@ With the `.env` file in place, the environment variables will be set every time
 
 Bridge Troll uses [Omniauth](https://github.com/intridea/omniauth) to allow external authentication to a number of services.
 
-* Twitter through [omniauth-twitter](https://github.com/arunagw/omniauth-twitter) - [set up a consumer here](https://apps.twitter.com/)
-* Facebook through [omniauth-facebook](https://github.com/mkdynamic/omniauth-facebook) - [set up a consumer here](https://developers.facebook.com/apps/)
-* GitHub through [omniauth-github](https://github.com/intridea/omniauth-github) - [set up a consumer here](https://github.com/settings/applications)
-* Meetup through [omniauth-meetup](https://github.com/tapster/omniauth-meetup) - [set up a consumer here](http://www.meetup.com/meetup_api/oauth_consumers/)
+- Twitter through [omniauth-twitter](https://github.com/arunagw/omniauth-twitter) - [set up a consumer here](https://apps.twitter.com/)
+- Facebook through [omniauth-facebook](https://github.com/mkdynamic/omniauth-facebook) - [set up a consumer here](https://developers.facebook.com/apps/)
+- GitHub through [omniauth-github](https://github.com/intridea/omniauth-github) - [set up a consumer here](https://github.com/settings/applications)
+- Meetup through [omniauth-meetup](https://github.com/tapster/omniauth-meetup) - [set up a consumer here](http://www.meetup.com/meetup_api/oauth_consumers/)
 
-To set up external authentication, create an oauth consumer on the site you want to authenticate with, then add [PROVIDER]_OAUTH_KEY and [PROVIDER]_OAUTH_SECRET value to the app environment.
+To set up external authentication, create an oauth consumer on the site you want to authenticate with, then add [PROVIDER]\_OAUTH_KEY and [PROVIDER]\_OAUTH_SECRET value to the app environment.
 
 When developing locally, it is often helpful to set up **local.bridgetroll.org** to point at your localhost server via your [hosts file](https://en.wikipedia.org/wiki/Hosts_%28file%29). You can then tell the OAuth provider to use the url local.bridgetroll.org. Often, a separate OAuth consumer needs to be set up for each environment (localhost/staging/production), but some providers (like Facebook) allow a consumer set up as "www.bridgetroll.org" to function for any subdomain (like "local.bridgetroll.org").
 
@@ -176,7 +186,9 @@ When you add a new OAuth consumer, set the _Website_ as `http://www.bridgetroll.
 The values for _key_ and _secret_ on the OAuth consumers page should be added to your local environment as MEETUP_OAUTH_KEY and MEETUP_OAUTH_SECRET, respectively.
 
 ## Contributors
+
 One billion thanks to our [super awesome contributors](https://github.com/railsbridge/bridge_troll/contributors).
 
 ## License
+
 The code is licensed under an [MIT license](https://github.com/railsbridge/bridge_troll/blob/master/LICENSE.md). Copyright (c) 2016 by RailsBridge.
diff --git a/app/controllers/events_controller.rb b/app/controllers/events_controller.rb
index 6aab37c36..331dc0938 100644
--- a/app/controllers/events_controller.rb
+++ b/app/controllers/events_controller.rb
@@ -12,7 +12,7 @@ def index
       format.html do
         @events = Event.upcoming.published_or_visible_to(current_user)
                        .includes(:location, :region, :chapter, :organization, event_sessions: :location)
-        @event_regions = @events.map(&:region).compact.uniq
+        @event_regions = @events.filter_map(&:region).uniq
       end
       format.json do
         render json: EventList.new(params[:type],
diff --git a/app/models/event.rb b/app/models/event.rb
index f2a96e32e..80d0961e1 100644
--- a/app/models/event.rb
+++ b/app/models/event.rb
@@ -334,7 +334,7 @@ def checked_in_attendees_other_dietary_restrictions
   end
 
   def other_dietary_restrictions_for(rsvps)
-    rsvps.map { |rsvp| rsvp.dietary_info.presence }.compact
+    rsvps.filter_map { |rsvp| rsvp.dietary_info.presence }
   end
 
   def organizer_names
diff --git a/nix/sources.json b/nix/sources.json
new file mode 100644
index 000000000..82cff1b0b
--- /dev/null
+++ b/nix/sources.json
@@ -0,0 +1,26 @@
+{
+    "niv": {
+        "branch": "master",
+        "description": "Easy dependency management for Nix projects",
+        "homepage": "https://github.com/nmattia/niv",
+        "owner": "nmattia",
+        "repo": "niv",
+        "rev": "af958e8057f345ee1aca714c1247ef3ba1c15f5e",
+        "sha256": "1qjavxabbrsh73yck5dcq8jggvh3r2jkbr6b5nlz5d9yrqm9255n",
+        "type": "tarball",
+        "url": "https://github.com/nmattia/niv/archive/af958e8057f345ee1aca714c1247ef3ba1c15f5e.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs": {
+        "branch": "release-20.03",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "1db42b7fe3878f3f5f7a4f2dc210772fd080e205",
+        "sha256": "05k9y9ki6jhaqdhycnidnk5zrdzsdammbk5lsmsbz249hjhhgcgh",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/1db42b7fe3878f3f5f7a4f2dc210772fd080e205.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    }
+}
diff --git a/nix/sources.nix b/nix/sources.nix
new file mode 100644
index 000000000..1938409dd
--- /dev/null
+++ b/nix/sources.nix
@@ -0,0 +1,174 @@
+# This file has been generated by Niv.
+
+let
+
+  #
+  # The fetchers. fetch_<type> fetches specs of type <type>.
+  #
+
+  fetch_file = pkgs: name: spec:
+    let
+      name' = sanitizeName name + "-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchurl { inherit (spec) url sha256; name = name'; }
+      else
+        pkgs.fetchurl { inherit (spec) url sha256; name = name'; };
+
+  fetch_tarball = pkgs: name: spec:
+    let
+      name' = sanitizeName name + "-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchTarball { name = name'; inherit (spec) url sha256; }
+      else
+        pkgs.fetchzip { name = name'; inherit (spec) url sha256; };
+
+  fetch_git = name: spec:
+    let
+      ref =
+        if spec ? ref then spec.ref else
+          if spec ? branch then "refs/heads/${spec.branch}" else
+            if spec ? tag then "refs/tags/${spec.tag}" else
+              abort "In git source '${name}': Please specify `ref`, `tag` or `branch`!";
+    in
+      builtins.fetchGit { url = spec.repo; inherit (spec) rev; inherit ref; };
+
+  fetch_local = spec: spec.path;
+
+  fetch_builtin-tarball = name: throw
+    ''[${name}] The niv type "builtin-tarball" is deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=tarball -a builtin=true'';
+
+  fetch_builtin-url = name: throw
+    ''[${name}] The niv type "builtin-url" will soon be deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=file -a builtin=true'';
+
+  #
+  # Various helpers
+  #
+
+  # https://github.com/NixOS/nixpkgs/pull/83241/files#diff-c6f540a4f3bfa4b0e8b6bafd4cd54e8bR695
+  sanitizeName = name:
+    (
+      concatMapStrings (s: if builtins.isList s then "-" else s)
+        (
+          builtins.split "[^[:alnum:]+._?=-]+"
+            ((x: builtins.elemAt (builtins.match "\\.*(.*)" x) 0) name)
+        )
+    );
+
+  # The set of packages used when specs are fetched using non-builtins.
+  mkPkgs = sources: system:
+    let
+      sourcesNixpkgs =
+        import (builtins_fetchTarball { inherit (sources.nixpkgs) url sha256; }) { inherit system; };
+      hasNixpkgsPath = builtins.any (x: x.prefix == "nixpkgs") builtins.nixPath;
+      hasThisAsNixpkgsPath = <nixpkgs> == ./.;
+    in
+      if builtins.hasAttr "nixpkgs" sources
+      then sourcesNixpkgs
+      else if hasNixpkgsPath && ! hasThisAsNixpkgsPath then
+        import <nixpkgs> {}
+      else
+        abort
+          ''
+            Please specify either <nixpkgs> (through -I or NIX_PATH=nixpkgs=...) or
+            add a package called "nixpkgs" to your sources.json.
+          '';
+
+  # The actual fetching function.
+  fetch = pkgs: name: spec:
+
+    if ! builtins.hasAttr "type" spec then
+      abort "ERROR: niv spec ${name} does not have a 'type' attribute"
+    else if spec.type == "file" then fetch_file pkgs name spec
+    else if spec.type == "tarball" then fetch_tarball pkgs name spec
+    else if spec.type == "git" then fetch_git name spec
+    else if spec.type == "local" then fetch_local spec
+    else if spec.type == "builtin-tarball" then fetch_builtin-tarball name
+    else if spec.type == "builtin-url" then fetch_builtin-url name
+    else
+      abort "ERROR: niv spec ${name} has unknown type ${builtins.toJSON spec.type}";
+
+  # If the environment variable NIV_OVERRIDE_${name} is set, then use
+  # the path directly as opposed to the fetched source.
+  replace = name: drv:
+    let
+      saneName = stringAsChars (c: if isNull (builtins.match "[a-zA-Z0-9]" c) then "_" else c) name;
+      ersatz = builtins.getEnv "NIV_OVERRIDE_${saneName}";
+    in
+      if ersatz == "" then drv else
+        # this turns the string into an actual Nix path (for both absolute and
+        # relative paths)
+        if builtins.substring 0 1 ersatz == "/" then /. + ersatz else /. + builtins.getEnv "PWD" + "/${ersatz}";
+
+  # Ports of functions for older nix versions
+
+  # a Nix version of mapAttrs if the built-in doesn't exist
+  mapAttrs = builtins.mapAttrs or (
+    f: set: with builtins;
+    listToAttrs (map (attr: { name = attr; value = f attr set.${attr}; }) (attrNames set))
+  );
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/lists.nix#L295
+  range = first: last: if first > last then [] else builtins.genList (n: first + n) (last - first + 1);
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L257
+  stringToCharacters = s: map (p: builtins.substring p 1 s) (range 0 (builtins.stringLength s - 1));
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L269
+  stringAsChars = f: s: concatStrings (map f (stringToCharacters s));
+  concatMapStrings = f: list: concatStrings (map f list);
+  concatStrings = builtins.concatStringsSep "";
+
+  # https://github.com/NixOS/nixpkgs/blob/8a9f58a375c401b96da862d969f66429def1d118/lib/attrsets.nix#L331
+  optionalAttrs = cond: as: if cond then as else {};
+
+  # fetchTarball version that is compatible between all the versions of Nix
+  builtins_fetchTarball = { url, name ? null, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchTarball;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchTarball ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
+      else
+        fetchTarball attrs;
+
+  # fetchurl version that is compatible between all the versions of Nix
+  builtins_fetchurl = { url, name ? null, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchurl;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchurl ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
+      else
+        fetchurl attrs;
+
+  # Create the final "sources" from the config
+  mkSources = config:
+    mapAttrs (
+      name: spec:
+        if builtins.hasAttr "outPath" spec
+        then abort
+          "The values in sources.json should not have an 'outPath' attribute"
+        else
+          spec // { outPath = replace name (fetch config.pkgs name spec); }
+    ) config.sources;
+
+  # The "config" used by the fetchers
+  mkConfig =
+    { sourcesFile ? if builtins.pathExists ./sources.json then ./sources.json else null
+    , sources ? if isNull sourcesFile then {} else builtins.fromJSON (builtins.readFile sourcesFile)
+    , system ? builtins.currentSystem
+    , pkgs ? mkPkgs sources system
+    }: rec {
+      # The sources, i.e. the attribute set of spec name to spec
+      inherit sources;
+
+      # The "pkgs" (evaluated nixpkgs) to use for e.g. non-builtin fetchers
+      inherit pkgs;
+    };
+
+in
+mkSources (mkConfig {}) // { __functor = _: settings: mkSources (mkConfig settings); }
diff --git a/shell.nix b/shell.nix
new file mode 100644
index 000000000..473abbc8f
--- /dev/null
+++ b/shell.nix
@@ -0,0 +1,14 @@
+let
+  sources = import ./nix/sources.nix { };
+  pkgs = import sources.nixpkgs { };
+in pkgs.mkShell {
+  buildInputs = [
+    # for nokogiri
+    pkgs.zlib
+    pkgs.libiconv
+    # for pg
+    pkgs.postgresql
+    #
+    pkgs.ruby_2_7
+  ];
+}
diff --git a/spec/mailers/previews/rsvp_preview.rb b/spec/mailers/previews/rsvp_preview.rb
index ac4016939..dd1a5998c 100644
--- a/spec/mailers/previews/rsvp_preview.rb
+++ b/spec/mailers/previews/rsvp_preview.rb
@@ -10,9 +10,9 @@ def reminder
   end
 
   def multiple_location_event_reminder
-    rsvp = EventSession.where.not(location_id: nil).all.map do |event_session|
+    rsvp = EventSession.where.not(location_id: nil).all.filter_map do |event_session|
       event_session.rsvps.where(role_id: Role::VOLUNTEER.id).first
-    end.compact.first
+    end.first
     RsvpMailer.reminder(rsvp)
   end