multipart/form upload Problem

[mj-jackson]

Hi all,

it seems like a bug to me, but I am not yet confident enough to post it as a bug, that's why I am asking here if I made a mistake.

With Cypress Version 6.2.0 the following code worked:

// commands.ts
Cypress.Commands.add('upload', {prevSubject: 'element'}, (element, file, fileName, type) => {
    const blob = Cypress.Blob.base64StringToBlob(file, type);
    const testFile = new File([blob], fileName, {type: type});

    cy.wrap(element).trigger('drop', {
        dataTransfer: {files: [testFile]},
    });
});

// my-test.spec.js
cy.fixture('path_to_fixture.xls', 'base64').then(content => {
  cy.get('dropzone').upload(content, 'my-excel.xls', 'application/vnd.ms-excel');
})

I wanted to update Cypress to 6.6.0 and found it didn't work again. Some downgrading later and the last version it worked actually was 6.2.0. Even the update to 6.2.1 breaks the code above.
I found this issue which was merged in 6.2.1: #9359
The issue sounds logical to me, but somehow it breaks my code (I guess).

More Info:
The file should get uploaded to a Spring Boot backend. A controller should accept the file with this method
upload(@RequestBody MultipartFile file)
But since the Cypress Version 6.2.1 file is always null, working flawlessly in 6.2.0 and also in normal work flow.

More more info:
I also tried the npm package cypress-file-upload, which also stopped working with 6.2.1.

Are there any steps I could take to further debug my situation. The logging in terms of files seems very limited.

Thanks