some custom field value in slack posts is not unformatted (#137)

* fix custom field formatting

* fix regression bug where NilReferenceError raised if a custom field value is nil

* fix indent

lib/redmine_slack/listener.rb

@@ -215,23 +215,27 @@ def channel_for_project(proj)
 	end
 
 	def detail_to_field(detail)
-		if detail.property == "cf"
-			key = CustomField.find(detail.prop_key).name rescue nil
+		case detail.property
+		when "cf"
+			custom_field = detail.custom_field
+			key = custom_field.name
 			title = key
-		elsif detail.property == "attachment"
+			value = (detail.value)? IssuesController.helpers.format_value(detail.value, custom_field) : ""
+		when "attachment"
 			key = "attachment"
 			title = I18n.t :label_attachment
+			value = escape detail.value.to_s
 		else
 			key = detail.prop_key.to_s.sub("_id", "")
 			if key == "parent"
 				title = I18n.t "field_#{key}_issue"
 			else
 				title = I18n.t "field_#{key}"
 			end
+			value = escape detail.value.to_s
 		end
 
 		short = true
-		value = escape detail.value.to_s
 
 		case key
 		when "title", "subject", "description"