Fluentd service is not starting correctly

Issue

• Fluentd doesn't start
• Fluentd can be started with root user but not with their own user
• The following traces can be seen in the log files:

Jan 09 00:55:19 compute-0.localdomain fluentd[178330]: /usr/share/rubygems/rubygems/path_support.rb:68:in `path=': undefined method `+' for nil:NilClass (NoMethodError)
Jan 09 00:55:19 compute-0.localdomain fluentd[178330]: from /usr/share/rubygems/rubygems/path_support.rb:30:in `initialize'
Jan 09 00:55:19 compute-0.localdomain fluentd[178330]: from /usr/share/rubygems/rubygems.rb:357:in `new'
Jan 09 00:55:19 compute-0.localdomain fluentd[178330]: from /usr/share/rubygems/rubygems.rb:357:in `paths'
Jan 09 00:55:19 compute-0.localdomain fluentd[178330]: from /usr/share/rubygems/rubygems.rb:379:in `path'
Jan 09 00:55:19 compute-0.localdomain fluentd[178330]: from /usr/share/rubygems/rubygems/specification.rb:794:in `dirs'
Jan 09 00:55:19 compute-0.localdomain fluentd[178330]: from /usr/share/rubygems/rubygems/specification.rb:658:in `each_normal'
Jan 09 00:55:19 compute-0.localdomain fluentd[178330]: from /usr/share/rubygems/rubygems/specification.rb:669:in `_all'