If a file with 0 bytes is dropped, then nothing happens. This is not very important but since 0 byte files do not provide a lot of information anyway, but for a user it might not be obvious that a file actually doesn't have any content. Thus at least a warning message should be displayed. Preferably the empty file should be uploaded (since it's the behaviour expected by the user). Then a message should be displayed that the file is empty to inform the user.
If a file with 0 bytes is dropped, then nothing happens. This is not very important but since 0 byte files do not provide a lot of information anyway, but for a user it might not be obvious that a file actually doesn't have any content. Thus at least a warning message should be displayed. Preferably the empty file should be uploaded (since it's the behaviour expected by the user). Then a message should be displayed that the file is empty to inform the user.