Drag&Drop mechanism not working if having required metadata

If you override File document type in order to add him required metadata, even if the metadata has default value, it will lead to being unable to use Drag&Drop for creating a File.

Reproduction steps:

1. Define "File" document type in your studio project
2. Add to it a new metadata
3. Define a default value for this metadata
4. Hotreload and try drag&drop: this should work fine
5. Specify the metadata as being required
6. Hotreload and try drag&drop: this should fail