fix(language-service): ignore null metadatas

[victornoel]

PR Checklist

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PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] angular.io application / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

See #20260.

Issue Number: #20260

What is the new behavior?

Ignore null metadatas.

It is a first proposition to start solving this annoying issue.
I suppose that if there are null metadatas, in general, it's better to ignore them than to fail in the language-service.
Concerning this particular bug (#20260), maybe I should also fix the fact that there are null metadata generated for locales? Tell me how to do that :)

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

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[victornoel]

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