This method registers the default task to perform if a mapping is not found.

• param string $method - The name of the method in the derived class to perform if a named task is not found.
• return \JControllerLegacy - A \JControllerLegacy object to support chaining.

public function registerDefaultTask($method)
 {
 $this->registerTask('__default', $method);

return $this;
 }