catching a rare error in clean_visible: a tiny tiny fraction of the kba-2012 "social" stream apparently has control characters or other invalid UTF8 chars, and we were treating this as text/plain which does not go through clean_html, so they were not getting caught before reaching serialization by lxml for tagging.
catching a rare error in clean_visible: a tiny tiny
fraction of the kba-2012 "social" stream apparently has control characters or other invalid UTF8
chars, and we were treating this as text/plain which does not go through clean_html, so they
were not getting caught before reaching serialization by lxml for tagging.

trec-kba/streamcorpus-pipeline,trec-kba/streamcorpus-pipeline,trec-kba/streamcorpus-pipeline