Subtle bug in features_get_default() if module_invoke() returns NULL

There's a subtle bug that shows up in features_get_default() for those rare occasions when module_invoke($m, $default_hook) returns NULL.

The Features code is as follows:

        if ($default_hook && module_hook($m, $default_hook)) {
          $cache[$component][$m] = module_invoke($m, $default_hook);
          if ($alter) {
            drupal_alter($default_hook, $cache[$component][$m]);
          }
        }

As you can see, this takes a default hook named $default_hook, checks to see if the current module $m contains this hook, if it does it then executes that module hook implementation and stores the return as $cache[$component][$m]. Simple stuff.

As an example consider flag.module. It's implementation of hook_views_default_views() starts with the following:

function flag_views_default_views() {
  // Only setup views for the "bookmarks" flag.
  // If it's been deleted, don't create any views.
  $flag = flag_get_flag('bookmarks');
  if (!$flag) {
    return;
  }

In this case, if there is not a flag named 'bookmarks' available it just bails and exits the function with a NULL return. The problem with the Features
logic in features_get_default() is that it doesn't check to see if the return from the hook implementation is valid, it immediately stores it in the $cache array and tries to run drupal_alter() on it.

Then skip on down the line to your own implementation of hook_views_default_views() and the normal expectation that $views is an array no longer is true, so using e.g. if(array_key_exists('myview', $views)) starts to throw errors like this:

warning: array_key_exists() [function.array-key-exists]: The second argument should be either an array or an object in sites/all/modules/Custom/mymodule/mymodule.module on line 1726.

Views' own implementation of this code is in the _views_discover_default_views() function and verifies that the results from the hook implementation was valid before trying to process it, as follows:

        $results = call_user_func($module . "_views_default_views");
        if (!empty($results) && is_array($results)) {

What I suggest is:

• Verifying that the results from the module_invoke() call is an array.
• If it is an array add it to the cache array and proceed.
• If it is not an array simply continue to the next iteration of the foreach() loop.

A patch will be forthcoming.