Grok's "match" throws "(TypeError) can't convert Array into String"

Exception in thread "LogStash::Runner" org.jruby.exceptions.RaiseException: (TypeError) can't convert Array into String
        at org.jruby.RubyString.+(org/jruby/RubyString.java:1112)
        at RUBY.initialize(file:/home/jumski/work/logstash-shell/files/logstash.jar!/logstash/filters/grok.rb:235)
        at RUBY.parse_config(file:/home/jumski/work/logstash-shell/files/logstash.jar!/logstash/agent.rb:333)
        at RUBY.parse(file:/home/jumski/work/logstash-shell/files/logstash.jar!/logstash/config/file.rb:53)
        at RUBY.each(file:/home/jumski/work/logstash-shell/files/logstash.jar!/logstash/config/file.rb:91)
        at org.jruby.RubyArray.each(org/jruby/RubyArray.java:1613)
        at RUBY.each(file:/home/jumski/work/logstash-shell/files/logstash.jar!/logstash/config/file.rb:90)
        at org.jruby.RubyHash.each(org/jruby/RubyHash.java:1257)
        at RUBY.each(file:/home/jumski/work/logstash-shell/files/logstash.jar!/logstash/config/file.rb:83)
        at RUBY.parse(file:/home/jumski/work/logstash-shell/files/logstash.jar!/logstash/config/file.rb:39)
        at RUBY.parse_config(file:/home/jumski/work/logstash-shell/files/logstash.jar!/logstash/agent.rb:323)
        at RUBY.run_with_config(file:/home/jumski/work/logstash-shell/files/logstash.jar!/logstash/agent.rb:427)
        at org.jruby.ext.thread.Mutex.synchronize(org/jruby/ext/thread/Mutex.java:149)
        at RUBY.run_with_config(file:/home/jumski/work/logstash-shell/files/logstash.jar!/logstash/agent.rb:426)
        at RUBY.run(file:/home/jumski/work/logstash-shell/files/logstash.jar!/logstash/agent.rb:373)
        at org.jruby.RubyProc.call(org/jruby/RubyProc.java:249)
        at RUBY.initialize(file:/home/jumski/work/logstash-shell/files/logstash.jar!/stud/task.rb:12)

input {                                                                                                                                 
  file {                                                                                                                                    path           => [ "/var/log/rails.log" ]                                                                                          
    type           => rails                                                                                                             
    format         => plain                                                                                                             
    start_position => beginning                                                                                                         
  }                                                                                                                                     
}                                                                                                                                       filter {                                                                                                                                  grok {                                                                                                                                
    type         => rails                                                                                                               
    patterns_dir => "/opt/logstash/patterns"                                                                                            
    match        => ["@message", "^Started"]                                                                                            
    pattern      => "%{RAILS_STARTED}"                                                                                                  
  }                                                                                                                                     
}                                                                                                                                       
output {                                                                                                                                  stdout {                                                                                                                              
    debug        => true                                                                                                                
    debug_format => json                                                                                                                
  }                                                                                                                                     
}