Recently the welcome script failed on Travis: https://travis-ci.org/wikimedia/pywikibot-core/jobs/58246884#L756 As that output is a bit unwieldy here is the output easier to read:
[NoAct] ***Ahmed abssi has no contributions. [Match] ***Brahhhimm has enough edits to be welcomed. WARNING: /home/travis/build/wikimedia/pywikibot-core/pywikibot/family.py:916: FamilyMaintenanceWarning: Family name wikimediachapter does not match family module name wikimedia SIMULATION: edit action blocked. *** Page [[ÙÙاش اÙ٠ستخد٠:Brahhhimm]] saved [Done ] ***One user has been welcomed. [NoAct] ***Hosnymansor has no contributions. [NoAct] ***Bilal chafi has no contributions. [NoAct] ***Ridouan al hannachi has no contributions. [NoAct] ***Techno oussama has no contributions. [NoAct] ***سÙ٠ا٠عبداÙرØÙ Ù Ù Ùس٠خبش has no contributions. [NoAct] ***Ø£Ø٠د عا٠ر اÙ٠طارÙØ© has no contributions. [NoAct] ***ÙÙÙÙ 000 has no contributions. [NoAct] ***Djoukeng Borel has no contributions. [NoAct] ***ArameaWiki has no contributions. [NoAct] ***Mjno0onk has no contributions. [NoAct] ***Abdulrmomin has no contributions. [NoAct] ***Amdsab has no contributions. [NoAct] ***WINNERS05 has no contributions. [NoAct] ***Super-hicham has no contributions. [NoAct] ***Badr salhi has no contributions. [NoAct] ***Amin osx has no contributions. [NoAct] ***Mohamed tahirii has no contributions. [NoAct] ***Sami almadhgi has no contributions. [NoAct] ***Wildtunis has no contributions. [Match] ***Achway has enough edits to be welcomed. [Skip ] ***Achway has been already welcomed. [NoAct] ***Anas x-love has no contributions. [NoAct] ***Cloracefmr has no contributions. [NoAct] ***Hamza halhoul has no contributions. [NoAct] ***Osama Alzoubi has no contributions. [NoAct] ***Ayoub malloul has no contributions. [NoAct] ***Turki althakafi has no contributions. [NoAct] ***7assiba has no contributions. [NoAct] ***El Ouakili has no contributions. [NoAct] ***TAREQ ESAM HAMMAD has no contributions. [NoAct] ***Jin dido has no contributions. [NoAct] ***Argentumbolo has no contributions. [NoAct] ***I'm so meta even this acronym has no contributions. [NoAct] ***Ikmalsyafiq has no contributions. [NoAct] ***Talal RH has no contributions. [NoAct] ***ابÙاÙاد5886 has no contributions. [NoAct] ***Malobaid has no contributions. [Match] ***John Vandenberg has enough edits to be welcomed. [Skip ] ***John Vandenberg has been already welcomed. [NoAct] ***XZise has no contributions. [NoAct] ***MZERYOH has no contributions. [NoAct] ***Aboomara1972 has no contributions. [NoAct] ***WÃ¥ Lîî Døx has no contributions. [NoAct] ***Ejs-80 has no contributions. [NoAct] ***Luke081515 has no contributions. [NoAct] ***س٠٠اÙبدر 502 has no contributions. [NoAct] ***MjdBashrahel has no contributions. [NoAct] ***Mohammed fanatsah has no contributions. [Skip ] ***دائرة اÙ٠عار٠اÙÙاÙÙÙÙØ© has been blocked! [NoAct] ***Latifa iman has no contributions. [MSG ] ***Putting the log of the latest user... [MSG ] ***Log page is not exist, getting information for page creation Traceback (most recent call last): File "/home/travis/build/wikimedia/pywikibot-core/pwb.py", line 215, in <module> run_python_file(filename, argv, argvu, file_package) File "/home/travis/build/wikimedia/pywikibot-core/pwb.py", line 84, in run_python_file main_mod.__dict__) File "./scripts/welcome.py", line 1017, in <module> main() File "./scripts/welcome.py", line 998, in main bot.run() File "./scripts/welcome.py", line 831, in run if self.makelogpage(self.welcomed_users): File "./scripts/welcome.py", line 661, in makelogpage text += u'\n!%s' % self.site.namespace(2) TypeError: unsupported operand type(s) for +=: 'NoneType' and 'unicode' CRITICAL: Waiting for 1 network thread(s) to finish. Press ctrl-c to abort
So text is None and looking into the code reveals that it translates it using the site's language and a fixed logpage_header table.
text = i18n.translate(self.site, logpage_header) text += u'\n!%s' % self.site.namespace(2)
And logpage_header has only the keys _default, no and it and without fallback set to True it won't use _default. Interestingly I can't find any recent changes that would've lead to this problem (e.g. fallback parameter removed).