_tp_connection_clean_up_handle_refs can be called with g_connection=NULL as a result of a Connection emitting the 'invalidated' signal. See https://bugzilla.redhat.com/attachment.cgi?id=325331 for an Empathy backtrace. This appears to have been caused by a Gabble crash.
It has been reported on Empathy with complete backtrace: http://bugzilla.gnome.org/show_bug.cgi?id=563105
Fixed in 0.7.20.
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