[Freeswitch-users] hangup_cause NONE vs. NORMAL_CLEARING

I have a small JS script that makes a call, plays a sound file and then hangs up. For each call it makes, I log the hangup_cause variable on the CHANNEL_HANGUP_COMPLETE event. Most of the time, when calls are successful, I get a NORMAL_CLEARING cause, but sometimes I'll get a NONE cause. I wanted to know what the difference between these two is, because there is no reference to NONE in the wiki (http://wiki.freeswitch.org/wiki/Hangup_causes ). Thanks, Nicolás