Notice: Trying to get property 'key' of non-object

[yellow1912]

This error happens on:

1. Symfony 4.4 latest
2. PHP 7.4
3. JMS TranslationBundle current master branch

The exact error is:

Trying to get property 'key' of non-object in file Translation/Extractor/File/FormExtractor.php
(I think there are 2 occurrences of this code in the same file)

if (!$item->key instanceof String_) {
                    continue;
                }

My guess is due to my code here:

[$bundles, ,] = $this->buildCache();

Not sure if it's somehow related to how the parser returns the node now? The easiest fix would be to check if $item is not null but I'm not sure if that's the correct fix.