Doctrine\OXM\OXMException::unknownEntityNamespace PHP Method

    public static function unknownEntityNamespace($entityNamespaceAlias)
    {
        return new self("Unknown Entity namespace alias '{$entityNamespaceAlias}'.");
    }

 /**
  * Resolves a registered namespace alias to the full namespace.
  *
  * @param string $entityNamespaceAlias
  * @return string
  * @throws MappingException
  */
 public function getEntityNamespace($entityNamespaceAlias)
 {
     if (!isset($this->_attributes['entityNamespaces'][$entityNamespaceAlias])) {
         throw OXMException::unknownEntityNamespace($entityNamespaceAlias);
     }
     return trim($this->_attributes['entityNamespaces'][$entityNamespaceAlias], '\\');
 }