Steps to Replicate

1. Edit a page.
2. Insert Files and Images from the Editor Toolbar.
3. Click on Upload Files and choose multiple files with one of them with 0 byte size.
   You can also choose multiple files with one of them with 0 byte size and drag into Confluence page.

Expected result:
All files is attached properly.

Actual Result:
The files before the "0 byte size file" attached properly:

The Length of stream must be greater than 0 ERROR appear for the "0 byte size file":

The remaining file after the "0 byte size file" stuck at waiting... and never get uploaded:

Workaround
Exclude the file with "0 byte size" from the upload list.