Index: chan_sip.c
===================================================================
--- chan_sip.c	(Revision 7817)
+++ chan_sip.c	(Arbeitskopie)
@@ -4715,7 +4715,7 @@
 	char iabuf[INET_ADDRSTRLEN];
 	const char *fromdomain;
 
-	if (p->rpid || p->rpid_from)
+	if (p->rpid != __ast_string_field_empty || p->rpid_from != __ast_string_field_empty)  
 		return;
 
 	if (p->owner && p->owner->cid.cid_num)
@@ -4917,7 +4917,7 @@
 	add_header(req, "CSeq", tmp);
 	add_header(req, "User-Agent", default_useragent);
 	add_header(req, "Max-Forwards", DEFAULT_MAX_FORWARDS);
-	if (p->rpid)
+	if (p->rpid != __ast_string_field_empty)
 		add_header(req, "Remote-Party-ID", p->rpid);
 }