honeypot_get_protected_forms cache not working properly

If using the honeypot module as an API (nothing configured in the UI) the honeypot_get_protected_forms() internal cache is not working, issuing a query statement on every request.

      // Look up all the honeypot forms in the variables table.
      $result = db_query("SELECT name FROM {variable} WHERE name LIKE 'honeypot_form_%'")->fetchCol();
      // Add each form that's enabled to the $forms array.
      foreach ($result as $variable) {
        if (variable_get($variable, 0)) {
          $forms[] = substr($variable, 14);
        }
      }

      // Save the cached data.
      cache_set('honeypot_protected_forms', $forms, 'cache');

In this code, if $result is empty, $forms will never be initialized (thus remaining NULL) and doing a cache_set with NULL data is not caching anything.

I propose to initialize the $forms array().

Patch attached.

What indeed makes sense would make the honeypot module just an "API", and the UI managed honeypot form alters be a submodule that can be optionally turned on, but that means refactoring the whole thing.

Many modules are now using this approach: separating the "coder" functionality from the "site builder" functionality.