[ckan-dev] Adding custom fields

[Milo Thurston]

Hello,
I’m trying out an installation of CKAN, and one thing that I need to do is add custom fields to datasets and resources. I’ve been following this tutorial here:
http://docs.ckan.org/en/latest/extensions/adding-custom-fields.html
I’ve performed all the steps except for the tag/tag vocabulary section, and can get the custom field to show up for datasets but not resources. I therefore wonder if there is something missing in the resources section or if I have made some mistake.
I’ve posted about this with a CKAN tag on Stack Overflow, where I’ve pasted some of the code:
http://stackoverflow.com/questions/26061386/adding-extra-fields-to-ckan-resources
One thing I didn’t spot earlier is that I can see the following in my apache logs:

[Mon Sep 29 11:24:54.865771 2014] [:error] [pid 2629] 2014-09-29 11:24:54,865 CRITI [ckan.helpers] Helper function `my_custom_fields` could not be found
[Mon Sep 29 11:24:54.865915 2014] [:error] [pid 2629]  (are you missing an extension?)

I’ve not defined the text “my_custom_fields” (it’s all “my_custom_field”) so I wonder where that’s coming from. 
Any suggestions would be welcome.
Thanks,
Milo Thurston.