Template filter date 'U' raises an AttributeError under certain circumstances
While fixing #10048 in  a new bug has been introduced. Around line 200 in django/utils/dateformat.py:
"Seconds since the Unix epoch (January 1 1970 00:00:00 GMT)"
off = self.timezone and self.timezone.utcoffset(self.data) or 0
return int(time.mktime(self.data.timetuple())) + off.seconds * 60
If self.timezone and self.timezone.utfoffset(self.data) evaluates to False, Django tries to access off.seconds but off is 0 => An AttributeError (int has no attribute seconds) is raised.
Unfortunately I do not know enough about the timezone handling to provide a test or even a fix.