When you visit https://www.mediawiki.org/wiki/Topic:Blah (invalid UUID) or https://www.mediawiki.org/wiki/Topic:S4tat94yjcpnz15m/flow (valid UUID, but with a subpage which is not how the Topic namespace works), you get a fatal:
"[8c125b71] 2014-11-14 23:08:54: Fatal exception of type Flow\Exception\InvalidInputException"
It should show a user-friendly error message.
Version: unspecified
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=68258