protected function _getDefinitionResolver(DefinitionInterface $definition)
    {
        $definitionType = get_class($definition);

        if (! isset($this->_definitionResolvers[$definitionType])) {
            throw new NotFoundException(
                "No definition resolver was configured for definition " .
                "of type $definitionType"
            );
        }

        return $this->_definitionResolvers[$definitionType];
    }