Remove casting in model - values should always be an array

Author: ElliottAYoung

app/models/tree_field_type.rb

@@ -11,7 +11,7 @@ def data=(data_hash)
     if values.is_a?(Hash)
       @values = values.keys
     else
-      @values = [values]
+      @values = values
     end
   end