the error is produced while rendering a form bound with POST data (since the form has errors it is being rendered again)
decompress method is not called in this case
value is not defined on self and the line 72
if self.value: is throwing error.
possible fix might be changing line 72 to if hasattr(self, 'value') and self.value:
wonder this kind of error is not being reported till now, am I missing something here ??