Comment 2 for bug 964729

StacktraceTop:
 g_hash_table_lookup_node (hash_return=<synthetic pointer>, key=0x23f0a19, hash_table=0x23bcd80) at /build/buildd/glib2.0-2.31.22/./glib/ghash.c:407
 g_hash_table_lookup_extended (hash_table=0x23bcd80, lookup_key=0x23f0a19, orig_key=0x0, value=0x0) at /build/buildd/glib2.0-2.31.22/./glib/ghash.c:1110
 on_cups_notification (connection=<optimized out>, sender_name=<optimized out>, object_path=<optimized out>, interface_name=<optimized out>, signal_name=<optimized out>, parameters=<optimized out>, user_data=0x7f6a10008600) at gsd-print-notifications-manager.c:558
 emit_signal_instance_in_idle_cb (data=0x7f6a08005150) at /build/buildd/glib2.0-2.31.22/./gio/gdbusconnection.c:3665
 g_main_dispatch (context=0x2215a10) at /build/buildd/glib2.0-2.31.22/./glib/gmain.c:2515