Exception when using -w or -x

[zidenis]

This exception is thrown when using sitegen -w or sitegen -x

$ sitegen -w
Found site_options in site.yaml: {author: zidenis, sasscompiler: sass, sass_path: [package:zengen, package:mdl], generator: SiteGen}
Observing (watch) .sitegen/html/_content...
Observing (watch) .sitegen/html/_templates...
Generating .html files...
   /index.html - done!
   /styles/main.scss - done!
Main SCSS: web/styles/main.scss
Compiling web/styles/main.scss -> web/styles/main.css
Unhandled exception:
ProcessException: No such file or directory
  Command: sassc web/styles/main.scss web/styles/main.css
#0      _ProcessImpl._runAndWait (dart:io-patch/process_patch.dart:449)
#1      _runNonInteractiveProcessSync (dart:io-patch/process_patch.dart:603)
#2      Process.runSync (dart:io-patch/process_patch.dart:64)
#3      Application._compileScss (package:sitegen/src/Application.dart:445)
#4      Application._compileSCSSFile (package:sitegen/src/Application.dart:337)
#5      Application.watchScss (package:sitegen/src/Application.dart:212)
#6      Application.run (package:sitegen/src/Application.dart:85)
#7      main (http://localhost:35549/sitegen.dart:5)
#8      _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:259)
#9      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:148)

Apparently, the problem is related to the SASS_PATH not set.

$ sitegen -s
Found site_options in site.yaml: {author: zidenis, sasscompiler: sass, sass_path: [package:zengen, package:mdl], generator: SiteGen}
Settings:
    Loglevel:                        info
    Content folder:                  .sitegen/html/_content
    Template folder:                 .sitegen/html/_templates
    Data folder:                     .sitegen/html/_data
    Partials folder:                 .sitegen/html/_partials
    Assets folder:                   .sitegen/html/_assets
    Default template:                default.html
    Output folder:                   web
    Workspace:                       .
    Dateformat:                      dd.MM.yyyy
    YAML-Delimeter:                  ~~~
    Use markdown:                    yes
    Use SASS:                        yes
    Use Autoprefixer:                yes
    Use secure connection:           no
    Cert-file for secure connection: dart.crt
    Key-file for secure connection:  dart.key
    Talk to me:                      no
    Site options:                    {author: zidenis, sasscompiler: sass, sass_path: [package:zengen, package:mdl], generator: SiteGen}
    Config folder:                   .sitegen
    Config file:                     site.yaml
    SASS compiler:                   sassc
    SASS_PATH (only for sass):       <not set>
    Browser:                         Chromium
    IP-Address:                      127.0.0.1
    Port:                            8080
    Document root:                   web
    Additional watchfolder1:         <not set>
    Additional watchfolder2:         <not set>
    Additional watchfolder3:         <not set>

My confs:

$ sass --version
Sass 3.4.23 (Selective Steve)
$ dart --version
Dart VM version: 1.22.1 (Tue Feb 21 14:27:26 2017) on "linux_x64"
$ pub global list
sitegen 1.6.4
stagehand 1.1.0
$ gem list --local

*** LOCAL GEMS ***

bigdecimal (default: 1.3.0)
bundler (1.14.6)
did_you_mean (1.1.0)
ffi (1.9.18)
io-console (default: 0.4.6)
json (default: 2.0.2)
minitest (5.10.1)
net-telnet (0.1.1)
openssl (default: 2.0.2)
power_assert (0.4.1)
psych (default: 2.2.2)
rake (12.0.0)
rdoc (default: 5.0.0)
sass (3.4.23)
sassc (1.11.2)
test-unit (3.2.3)
xmlrpc (0.2.1)

Any clue?