public function findShell($shell)
{
$className = $this->_shellExists($shell);
if (!$className) {
$shell = $this->_handleAlias($shell);
$className = $this->_shellExists($shell);
}
if (!$className) {
throw new MissingShellException(['class' => $shell]);
}
return $this->_createShell($className, $shell);
}