johnpaulett/twisted-hl7 — pull request #7 by rectalogic (2014-10-23 15:36:39+00:00)
Title: mllp errback should return the failure to prevent callbacks continuing t...

...o be called after the error.

"Note: If an errback doesn’t return anything, then it effectively returns None , meaning that callbacks will continue to be executed after this errback."
https://twistedmatrix.com/documents/current/core/howto/defer.html#errbacks