Events sometimes emitted with undefined file

[mifi]

This has caused many errors like «cannot read properies of undefined» in the wild. I think we should prevent events from being emitted after a file has been set to undefined. See #3811

Event that sometimes get emitted with file argument undefined:

• [ ] upload-error
• [ ] upload-started
• [ ] upload-progress
• [ ] upload-success
• [ ] preprocess-progress
• [ ] preprocess-complete
• [ ] postprocess-progress
• [ ] postprocess-complete
• [ ] dashboard:file-edit-complete
• [ ] file-added
• [ ] file-removed

So we need to search for all occurrences of each of these, and make sure that we don't emit an undefined file argument.

For example here: https://github.com/transloadit/uppy/blob/3121fae11b0907b804219baa8676f646353bd821/packages/%40uppy/transloadit/src/index.js#L619

we should probably return before emitting any events, or maybe better make sure files are only ever deleted after an upload has finished or failed.

[Murderlon]

Can we make this issue more specific? It's not really actionable at the moment.

[mifi]

I updated the description

[heloineto]

When does this happen?

Is it when the user deletes the file before it's finished uploading?

[Murderlon]

We haven't seen this happen anymore so the issue is not reproducible. Luckily we are migrating everything to TS, then we can make sure things are happening correctly.