Fixed null safety error in getData()

[timcreatedit]

When attempting to call the getData() method on a nonexistent Reference a CastError is currently thrown due to the method erroneously having a non-nullable type while the original library allows for null to be returned. This PR fixes this problem, so that for example getting the data of a file that wasn't written yet can be unit tested properly.

[atn832]

Looks good. Would you mind also adding a unit test that shows the new behavior? It'll also prevent people from accidentally breaking your change in the future.

[timcreatedit]

I've added two tests for the getData() method, one of which failed before the change and passes now :)

[timcreatedit]

@atn832 During my testing I also noticed, that the behavior for .child() is inconsistent with the actual CloudFirestore package. It doesn't add a "/" to the path. I also fixed that in the latest commit

[atn832]

@atn832 During my testing I also noticed, that the behavior for .child() is inconsistent with the actual CloudFirestore package. It doesn't add a "/" to the path. I also fixed that in the latest commit

Thank you for attempting to fix this bug as well. However, we want to keep each PR specific to one issue. Otherwise PRs grow large and they become harder to review. Since they are harder to review, it takes more time, and we may accidentally introduce new bugs. If we stick to one issue, we can merge the PR much faster and more safely.

Also, if some PR causes a regression, it is much easier to revert just that one PR instead of a huge PR that will revert some real fixes and one regression.

I filed #28 so that you can fix it in a separate PR, if you wish to.

For this PR, would you mind reverting the fix to .child()?

[atn832]

The tests look good. One final ask: can you remove the unused import in the tests and the changes to .child()?

[timcreatedit]

I've made the changes you requested, sorry it took me so long 😬

[atn832]

The analyzer job failed with:

info • Only use double quotes for strings containing single quotes • test/firebase_storage_mocks_test.dart:51:50 • prefer_single_quotes

I'll merge it anyway. Please do fix it later when you get the chance. :)

Thank you for the PR.