diff --git a/.gitignore b/.gitignore
index bd8b459..3a93b4e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,4 @@
 coverage
 tmp
-Gemfile
 .svn
 .directory
diff --git a/Gemfile b/Gemfile
new file mode 100644
index 0000000..5f15932
--- /dev/null
+++ b/Gemfile
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+source 'https://rubygems.org' do
+  gem 'sorted_set'
+end
diff --git a/init.rb b/init.rb
index 77bce7d..1dd9151 100644
--- a/init.rb
+++ b/init.rb
@@ -16,9 +16,11 @@
 
 #RedmineApp::Application.config.after_initialize do
 Rails.application.config.to_prepare do
-  require_dependency 'ldap_sync/core_ext'
-  require_dependency 'ldap_sync/infectors'
+  require "#{File.dirname(__FILE__)}/lib/ldap_sync/core_ext"
+  require "#{File.dirname(__FILE__)}/lib/ldap_sync/infectors"
 end
 
 # hooks
-require_dependency 'ldap_sync/hooks'
+require "#{File.dirname(__FILE__)}/lib/ldap_sync/hooks"
+
+require "#{File.dirname(__FILE__)}/lib/ldap_sync/infectors"
diff --git a/lib/ldap_sync/core_ext.rb b/lib/ldap_sync/core_ext.rb
index 61d626c..0463820 100644
--- a/lib/ldap_sync/core_ext.rb
+++ b/lib/ldap_sync/core_ext.rb
@@ -15,4 +15,8 @@
 #
 # You should have received a copy of the GNU General Public License
 # along with Redmine LDAP Sync.  If not, see <http://www.gnu.org/licenses/>.
-Dir[File.dirname(__FILE__) + "/core_ext/*.rb"].each { |file| require(file) }
\ No newline at end of file
+module LdapSync
+  class CoreExt
+    Dir[File.dirname(__FILE__) + "/core_ext/*.rb"].each { |file| require(file) }
+  end
+end
\ No newline at end of file
diff --git a/lib/ldap_sync/core_ext/ber.rb b/lib/ldap_sync/core_ext/ber.rb
index 72ce308..9838a98 100644
--- a/lib/ldap_sync/core_ext/ber.rb
+++ b/lib/ldap_sync/core_ext/ber.rb
@@ -15,48 +15,54 @@
 #
 # You should have received a copy of the GNU General Public License
 # along with Redmine LDAP Sync.  If not, see <http://www.gnu.org/licenses/>.
-if ('0.12.0'..'0.13.0') === Gem.loaded_specs['net-ldap'].version.to_s
-  require 'net/ber'
+module LdapSync
+  class CoreExt
+    class Ber
+      if ('0.12.0'..'0.13.0') === Gem.loaded_specs['net-ldap'].version.to_s
+        require 'net/ber'
 
-  ##
-  # A String object with a BER identifier attached.
-  #
-  class Net::BER::BerIdentifiedString < String
-    attr_accessor :ber_identifier
+        ##
+        # A String object with a BER identifier attached.
+        #
+        class Net::BER::BerIdentifiedString < String
+          attr_accessor :ber_identifier
 
-    # The binary data provided when parsing the result of the LDAP search
-    # has the encoding 'ASCII-8BIT' (which is basically 'BINARY', or 'unknown').
-    #
-    # This is the kind of a backtrace showing how the binary `data` comes to
-    # BerIdentifiedString.new(data):
-    #
-    #  @conn.read_ber(syntax)
-    #     -> StringIO.new(self).read_ber(syntax), i.e. included from module
-    #     -> Net::BER::BERParser.read_ber(syntax)
-    #        -> (private)Net::BER::BERParser.parse_ber_object(syntax, id, data)
-    #
-    # In the `#parse_ber_object` method `data`, according to its OID, is being
-    # 'casted' to one of the Net::BER:BerIdentifiedXXX classes.
-    #
-    # As we are using LDAP v3 we can safely assume that the data is encoded
-    # in UTF-8 and therefore the only thing to be done when instantiating is to
-    # switch the encoding from 'ASCII-8BIT' to 'UTF-8'.
-    #
-    # Unfortunately, there are some ActiveDirectory specific attributes
-    # (like `objectguid`) that should remain binary (do they really?).
-    # Using the `#valid_encoding?` we can trap this cases. Special cases like
-    # Japanese, Korean, etc. encodings might also profit from this. However
-    # I have no clue how this encodings function.
-    def initialize args
-      super
-      #
-      # Check the encoding of the newly created String and set the encoding
-      # to 'UTF-8' (NOTE: we do NOT change the bytes, but only set the
-      # encoding to 'UTF-8').
-      current_encoding = encoding
-      if current_encoding == Encoding::BINARY
-        force_encoding('UTF-8')
-        force_encoding(current_encoding) unless valid_encoding?
+          # The binary data provided when parsing the result of the LDAP search
+          # has the encoding 'ASCII-8BIT' (which is basically 'BINARY', or 'unknown').
+          #
+          # This is the kind of a backtrace showing how the binary `data` comes to
+          # BerIdentifiedString.new(data):
+          #
+          #  @conn.read_ber(syntax)
+          #     -> StringIO.new(self).read_ber(syntax), i.e. included from module
+          #     -> Net::BER::BERParser.read_ber(syntax)
+          #        -> (private)Net::BER::BERParser.parse_ber_object(syntax, id, data)
+          #
+          # In the `#parse_ber_object` method `data`, according to its OID, is being
+          # 'casted' to one of the Net::BER:BerIdentifiedXXX classes.
+          #
+          # As we are using LDAP v3 we can safely assume that the data is encoded
+          # in UTF-8 and therefore the only thing to be done when instantiating is to
+          # switch the encoding from 'ASCII-8BIT' to 'UTF-8'.
+          #
+          # Unfortunately, there are some ActiveDirectory specific attributes
+          # (like `objectguid`) that should remain binary (do they really?).
+          # Using the `#valid_encoding?` we can trap this cases. Special cases like
+          # Japanese, Korean, etc. encodings might also profit from this. However
+          # I have no clue how this encodings function.
+          def initialize args
+            super
+            #
+            # Check the encoding of the newly created String and set the encoding
+            # to 'UTF-8' (NOTE: we do NOT change the bytes, but only set the
+            # encoding to 'UTF-8').
+            current_encoding = encoding
+            if current_encoding == Encoding::BINARY
+              force_encoding('UTF-8')
+              force_encoding(current_encoding) unless valid_encoding?
+            end
+          end
+        end
       end
     end
   end
diff --git a/lib/ldap_sync/core_ext/file_store.rb b/lib/ldap_sync/core_ext/file_store.rb
index e663e4d..bf35f07 100644
--- a/lib/ldap_sync/core_ext/file_store.rb
+++ b/lib/ldap_sync/core_ext/file_store.rb
@@ -15,12 +15,18 @@
 #
 # You should have received a copy of the GNU General Public License
 # along with Redmine LDAP Sync.  If not, see <http://www.gnu.org/licenses/>.
-class ActiveSupport::Cache::FileStore
-  def delete_unless
-    options = merged_options(options)
-    search_dir(cache_path) do |path|
-      key = file_path_key(path)
-      delete_entry(key, options) unless yield(key)
+module LdapSync
+  class CoreExt
+    class FileStore
+      class ActiveSupport::Cache::FileStore
+        def delete_unless
+          options = merged_options(options)
+          search_dir(cache_path) do |path|
+            key = file_path_key(path)
+            delete_entry(key, options) unless yield(key)
+          end
+        end
+      end
     end
   end
 end
\ No newline at end of file
diff --git a/lib/ldap_sync/core_ext/ldap.rb b/lib/ldap_sync/core_ext/ldap.rb
index 92090d5..66d33d2 100644
--- a/lib/ldap_sync/core_ext/ldap.rb
+++ b/lib/ldap_sync/core_ext/ldap.rb
@@ -17,8 +17,15 @@
 # along with Redmine LDAP Sync.  If not, see <http://www.gnu.org/licenses/>.
 require 'net/ldap'
 
-class Net::LDAP
-  if Gem.loaded_specs['net-ldap'].version < Gem::Version.new('0.12.0')
-    Error = LdapError
+module LdapSync
+  class CoreExt
+    class Ldap
+
+      class Net::LDAP
+        if Gem.loaded_specs['net-ldap'].version < Gem::Version.new('0.12.0')
+          Error = LdapError
+        end
+      end
+    end
   end
 end
\ No newline at end of file
diff --git a/lib/ldap_sync/core_ext/ldap_entry.rb b/lib/ldap_sync/core_ext/ldap_entry.rb
index 329493f..7111c14 100644
--- a/lib/ldap_sync/core_ext/ldap_entry.rb
+++ b/lib/ldap_sync/core_ext/ldap_entry.rb
@@ -17,8 +17,14 @@
 # along with Redmine LDAP Sync.  If not, see <http://www.gnu.org/licenses/>.
 require 'net/ldap'
 
-class Net::LDAP
-  class Entry
-    include Enumerable
+module LdapSync
+  class CoreExt
+    class LdapEntry
+      class Net::LDAP
+        class Entry
+          include Enumerable
+        end
+      end
+    end
   end
 end
\ No newline at end of file
diff --git a/lib/ldap_sync/core_ext/migration.rb b/lib/ldap_sync/core_ext/migration.rb
index dd0861f..0b63052 100644
--- a/lib/ldap_sync/core_ext/migration.rb
+++ b/lib/ldap_sync/core_ext/migration.rb
@@ -15,12 +15,18 @@
 #
 # You should have received a copy of the GNU General Public License
 # along with Redmine LDAP Sync.  If not, see <http://www.gnu.org/licenses/>.
-class ActiveRecord::Migration
-    unless defined? self.[]
-        
-        # Enables the use of versioned migrations on rails < 5
-        def self.[](version)
-            self
-        end
+module LdapSync
+  class CoreExt
+    class Migration
+      class ActiveRecord::Migration
+          unless defined? self.[]
+
+              # Enables the use of versioned migrations on rails < 5
+              def self.[](version)
+                  self
+              end
+          end
+      end
     end
+  end
 end
\ No newline at end of file
diff --git a/lib/ldap_sync/core_ext/string.rb b/lib/ldap_sync/core_ext/string.rb
index 690ada2..223a0ec 100644
--- a/lib/ldap_sync/core_ext/string.rb
+++ b/lib/ldap_sync/core_ext/string.rb
@@ -17,13 +17,19 @@
 # along with Redmine LDAP Sync.  If not, see <http://www.gnu.org/licenses/>.
 require 'net/ldap'
 
-module Net::BER::Extensions::String
-  if Gem.loaded_specs['net-ldap'].version < Gem::Version.new('0.12.0')
-    def raw_utf8_encoded
-      if self.respond_to?(:encode) && self.encoding.name != 'ASCII-8BIT'
-        self.encode('UTF-8').force_encoding('ASCII-8BIT')
-      else
-        self
+module LdapSync
+  class CoreExt
+    class String
+      module Net::BER::Extensions::String
+        if Gem.loaded_specs['net-ldap'].version < Gem::Version.new('0.12.0')
+          def raw_utf8_encoded
+            if self.respond_to?(:encode) && self.encoding.name != 'ASCII-8BIT'
+              self.encode('UTF-8').force_encoding('ASCII-8BIT')
+            else
+              self
+            end
+          end
+        end
       end
     end
   end
diff --git a/lib/ldap_sync/entity_manager.rb b/lib/ldap_sync/entity_manager.rb
index e049699..60cfcc4 100644
--- a/lib/ldap_sync/entity_manager.rb
+++ b/lib/ldap_sync/entity_manager.rb
@@ -35,7 +35,7 @@ def get_user_fields(username, user_data=nil, options={})
       end
       return {} if user_data.nil?
 
-      user_fields = user_data.inject({}) do |fields, (attr, value)|
+      user_fields = user_data.to_h.inject({}) do |fields, (attr, value)|
         f = setting.user_field(attr)
         if f && fields_to_sync.include?(f)
           fields[f] = value.first unless value.nil? || value.first.blank?
@@ -103,8 +103,8 @@ def ldap_users
           end
         end
 
-        changes[:enabled].delete(nil)
-        changes[:locked].delete(nil)
+        changes[:enabled].delete("")
+        changes[:locked].delete("")
 
         users_on_local = self.users.active.map {|u| u.login.downcase }
         users_on_ldap = changes.values.sum.map(&:downcase)