Check if PDU Session has no session graph

src/smf_app/smf_context.cpp

@@ -3493,6 +3493,16 @@ bool smf_context::handle_ho_preparation_request(
     return false;
   }
 
+  if(!sp->get_sessions_graph()){
+    //abnormal condition when the PDU Session has no associate graph
+      //TODO: Check correct return code/error
+    smf_app_inst->trigger_update_context_error_response(
+        http_status_code_e::HTTP_STATUS_CODE_403_FORBIDDEN,
+        PDU_SESSION_APPLICATION_ERROR_NETWORK_FAILURE,
+        sm_context_request.get()->pid);
+    return false; 
+  }
+
   edge access_upf = 
       sp->get_sessions_graph()->get_access_edge();