I am not sure that I understand what you mean. Can you explain what you expected and what happened instead?

@xabbuh here is the reproducer https://github.com/BoShurik/symfony-file-bag-issue

When you submit form without uploading files, collection with FileTypes resets. I expect to get nulls for not uploaded files.

If I understand your concerns correctly, this is just how handling HTML forms work here. If you do not select a file to be uploaded, the client will not send any data for it so it even won't be null on the side where the Form component is doing its job.

So I am going to close here as there is nothing we can change in the component.

If I understood you wrong, please leave a comment with some more explanation and we can consider to reopen.

Problem in HttpFoundation component.

<input type="file" name="single">
<input type="file" name="multiple[]" multiple="multiple">

<input type="file" name="array[0]">
<input type="file" name="array[1]">

<input type="file" name="hash[key0]">
<input type="file" name="hash[key1]">

dump($request->files->get('single')); // null
dump($request->files->get('multiple')); // []
dump($request->files->get('array')); // []
dump($request->files->get('hash')); // { key1 => null, key2 => null }

hash and single receive nulls

The problem is that client do send data: UPLOAD_ERR_NO_FILE - is what I need.

As I can see #24198 was introduced to fix FileType with multiple => true

This causes a problem later when using FileType with multiple option - if no files are sent the form data are [0 => ''] instead of [].

I tried to remove changes made in that PR and all tests in Form component are pass,
FileType with multiple => true is produce correct result ([]) with empty file

dump($request->files->get('single')); // null
dump($request->files->get('multiple')); // [ 0 => null]
dump($request->files->get('array')); // [ 0 => null, 1 => null]
dump($request->files->get('hash')); // { key1 => null, key2 => null }

Does this change considered as a BC break? If so, maybe you know a workaround?
I tried to use string keys for a collection (with DataTransformer) but looks like it is ignored in ResizeFormListener

@xabbuh filtering $request->files can be easily achieved in resulting application, but it's impossible to unfilter it