Undefined index: {file_style} in _file_entity_tokens_get_property()

Coming back to my initial issue
$value = isset($info[$file['fid']][$property]) ?: NULL;
I'm not expert on shorthand php but should it be rather like this ? Previous version will return TRUE instead of a value, no ?
$value = isset($info[$file['fid']][$property]) ? $info[$file['fid']][$property]: NULL;

But I think the problem is a lit bit more complex.
$property is supposed to be one of the imagecache indexes, e.g. thumbnail, large, etc.
The isset test avoids the Undefined index warning but this is not normal to get an undefined value there as the imagecache types exist but just they aren't never carried by the $info[$file]['fid'] array into the _file_entity_tokens_get_property() function. Also here is another error message related to entity_token and to this lack of $property value. There is an "Notice : Array to string conversion in token_replace() (line 102..." error which comes together with (after) the "Undefined index: {file_style} in _file_entity_tokens_get_property" error. This happens only with media image fields (media entity files), and there are no errors with drupal image field. Additionally, any image related metatag results to "http://www.sitename.com/Array"

Digging further it appears that in token_generate() (in core token.inc) we get two tokens of the same index. Here is the final result after call to module_invoke_all by token_generate:

$replacements =  array('[node:field_media:thumbnail]' => 
  array (
    0 => NULL,
    1 => 'http://www.sitename.com/sites/default/files/styles/thumbnail/public/media/image/article/2002/10/article_image.jpg?itok=xxxxxx',
  ),
)

The first (indexed 0) NULL value comes from file_entity_tokens() hook processing "field_media:thumbnail", while the second (indexed 1) value seems to be generated by the imagecache_token module.

Finally I think there is a problem either with the properties definitions at file_entity_token_info() or with the testings on file types inside file_entity_tokens() but I can't figure exactly where.

As a temporary solution, I conditioned the return of file_entity_tokens to NOT provide a replacement token if the value is NULL

          if (is_array($return)) {
            $search_tokens = token_find_with_prefix($tokens, $field_name);
            if ($array_tokens = token_find_with_prefix($search_tokens, $property)) {
              $replacements += token_generate('array', $array_tokens, array('array' => $return), $options);
            }
          }
          else {
	    if ($return !== NULL)
              $replacements[$original] = $return;
          }

Seems to work with no errors in the logs and with my image metatags generated although.