Exception needed in encoder.total_len when all if conditions are False (requests_toolbelt)

[BookWorm0]

If I attempt to upload using a fileobj which does not contain one of the attributes which provide its length, total_len() returns None. This then leads to an exception being raised with the confusing message, “TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'” (encoder.py, line 488, in init).

It would be helpful if total_len() raised an exception which identified the problem as a fileobj which could not provide the package its content length.