FS-4776 forgot to push this

src/mod/endpoints/mod_dingaling/mod_dingaling.c

@@ -4186,7 +4186,7 @@ static ldl_status handle_signalling(ldl_handle_t *handle, ldl_session_t *dlsessi
 				tech_pvt->them = switch_core_session_strdup(session, ldl_session_get_callee(dlsession));
 				tech_pvt->us = switch_core_session_strdup(session, ldl_session_get_caller(dlsession));
 
-				if ((tmp = strdup(tech_pvt->us))) {
+				if (tech_pvt->us && (tmp = strdup(tech_pvt->us))) {
 					char *p, *q;
 
 					if ((p = strchr(tmp, '@'))) {