final protected function statementList(array! statements, bool extendsMode = false) -> string

It sometimes returns null which leads to the crash:

PHP Fatal error: Phalcon\Mvc\View\Engine\Volt\Compiler::statementList(): Return value must be of type string, null returned

Also similar on the readMetaDataIndex function
PHP Fatal error: Phalcon\Mvc\Model\MetaData::readMetaDataIndex(): Return value must be of type ?array, string returned