When a property isn't set or isn't available, it's better to say it's `null` than `false`.

tag-dropdown-widget.php

@@ -85,7 +85,7 @@ class taxonomy_dropdown_widget_plugin {
 		if ( 'option_defaults' == $var )
 			return $this->option_defaults;
 
-		return false;
+		return null;
 	}
 
 	/**