diff --git a/coreapi/linphonecore.c b/coreapi/linphonecore.c
index 6b8a79661..e37d47c72 100644
--- a/coreapi/linphonecore.c
+++ b/coreapi/linphonecore.c
@@ -1874,7 +1874,7 @@ static void apply_user_agent(LinphoneCore *lc){
 void linphone_core_set_user_agent(LinphoneCore *lc, const char *name, const char *ver){
 #if USE_BELLESIP
 	char ua_string[256];
-	snprintf(ua_string, sizeof(ua_string) - 1, "%s/%s", name, ver);
+	snprintf(ua_string, sizeof(ua_string) - 1, "%s/%s", name?name:"", ver?ver:"");
 	if (lc->sal) {
 		sal_set_user_agent(lc->sal, ua_string);
 		sal_append_stack_string_to_user_agent(lc->sal);
diff --git a/tester/message_tester.c b/tester/message_tester.c
index 66c75df86..cf99c1013 100644
--- a/tester/message_tester.c
+++ b/tester/message_tester.c
@@ -33,9 +33,11 @@ void text_message_received(LinphoneCore *lc, LinphoneChatRoom *room, const Linph
 void message_received(LinphoneCore *lc, LinphoneChatRoom *room, LinphoneChatMessage* message) {
 	char* from=linphone_address_as_string(linphone_chat_message_get_from(message));
 	stats* counters;
-	ms_message("Message from [%s]  is [%s] , external URL [%s]",from
-																,linphone_chat_message_get_text(message)
-																,linphone_chat_message_get_external_body_url(message));
+	const char *text=linphone_chat_message_get_text(message);
+	const char *external_body_url=linphone_chat_message_get_external_body_url(message);
+	ms_message("Message from [%s]  is [%s] , external URL [%s]",from?from:""
+																,text?text:""
+																,external_body_url?external_body_url:"");
 	ms_free(from);
 	counters = get_stats(lc);
 	counters->number_of_LinphoneMessageReceived++;