Some custom contexts may not have token entity mappings

Hi guys,

Thanks very much for the great work on the API and following up with the bug fixing.

I just wanted to report a minor issue I encountered while working with the latest versions of the metatag [7.x-1.0-beta4+19-dev (2012-12-06)] and metatag_views [sandbox] modules.

This is also related with #1830952: Introduce two new hooks to allow token types and patterns alteration somehow, since it's related with tokens and token types.

In file metatag.admin.inc, line 276, function metatag_config_edit_form:

  if ($contexts[0] != 'global') {
    $options['token types'] = array(token_get_entity_mapping('entity', $contexts[0]));
  }

So in this particular use case with the metatag_views module, which introduces a views context, is not global and has no entity mappings, the call token_get_entity_mapping('entity', 'views'); returns FALSE.
As a result, $options['token types'] = array(0 =>FALSE); is passed to metatag_metatags_form($form, $config->instance, $config->config, $options); Through the $options parameter.

So I thought perhaps we would want to avoid adding any value to the $options['token types'] array if the function token_get_entity_mapping returned FALSE.

In general, I would assume this could happen not only with the metatag_views (ribakker) (that I have tested), views_metatags (Dave Reid), but I would assume any module that implements a context/config that isn't an entity mapped with tokens or global.

This would matter as well for: #1830952: Introduce two new hooks to allow token types and patterns alteration since, it's introducing a hook to alter token types (see: drupal_alter('metatag_token_types', $options['token types']);) that would have a FALSE value in it instead of being empty, for example.

Please find attached to this ticket a patch that attempts to resolve this issue:
metatag-custom-contexts-not-have-token-mappings-0.patch
I tried to add few words in a comment to explain this aspect of the logic.

Could you please let me know if I overlooked or missed anything in the current metatag module (and its API), in terms of whether this would be a problem or not?

Please let me know if you would have any questions on any points/code/aspects mentioned in this ticket, I would surely be glad to provide more information.

I would greatly appreciate if you could take a bit of time to look into the patch and give me your feedback/opinion on this issue.

Any feedback, testing, changes, recommendations would be highly appreciated.
Thanks in advance.