GitLab

- Clear up a comment

- Rename 'keys, values' to 'key, value'

- Fix potential bug: If the default for a given form entry is a list, but
  the form provided only one value (and didn't indicate it should be a list
  with :list), appending the defaults would fail.

- Fix bug: If the default is a list of primitive items (not records), none
  of them would be added to the form field due to the use of the wrong
  (potentially non-existing) variable name.

- Use isinstance(var, lt) instead of type(var) == type([]).