Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 149920)
+++ channels/chan_sip.c	(working copy)
@@ -11907,6 +11907,11 @@
 		return -1;
 	}
 
+	if (!chan) {
+		ast_log(LOG_WARNING, "This function requires a channel.\n");
+		return NULL;
+	}
+
 	ast_channel_lock(chan);
 	if (chan->tech != &sip_tech && chan->tech != &sip_tech_info) {
 		ast_log(LOG_WARNING, "This function can only be used on SIP channels.\n");