Prevent internal server error if empty custom field for channel (refs #17)

README.md

@@ -24,7 +24,11 @@ from the plugin directory.
 
 Restart Redmine, and you should see the plugin show up in the Plugins page.
 Under the configuration options, set the Mattermost API URL to the URL for an
-Incoming WebHook integration in your Mattermost account (see also the next two sections).
+Incoming WebHook integration in your Mattermost account and also set the Mattermost
+Channel to the channel's handle (be careful, this is not the channel's display name
+visible to users, you can find each channel's handle by navigating inside the channel
+and clicking the down-arrow and selecting view info). See also the next two sections
+for advanced and custom routing options.
 
 ## Customized Routing
 

lib/redmine_mattermost/listener.rb

@@ -202,7 +202,8 @@ private
 			Setting.plugin_redmine_mattermost[:channel],
 		].find{|v| v.present?}
 
-		# Channel name '-' is reserved for NOT notifying
+		# Channel name '-' or empty '' is reserved for NOT notifying
+		return [] if val.to_s == ''
 		return [] if val.to_s == '-'
 		val.split(",")
 	end