Fix bug 2399: vnf instantiation parameters could have no vdu params

This change fixes bug 2399 that was reported in relation a multi-site
NS deployment. However, this issue could appear in multiple
circumstances, whenever there are vnf instantiation parameters and there
are no vdu params inside.

Change-Id: Id6d3c0b88a2a8478e1908372b24e3d13cdb94dcf
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/osm_nbi/instance_topics.py b/osm_nbi/instance_topics.py
index 3eb14d2..607dc73 100644
--- a/osm_nbi/instance_topics.py
+++ b/osm_nbi/instance_topics.py
@@ -377,7 +377,7 @@
             elif ns_request.get("vnf"):
                 vnf_data = ns_request.get("vnf")
                 for vnf in vnf_data:
-                    for vdu in vnf.get("vdu"):
+                    for vdu in vnf.get("vdu", []):
                         if vdu.get("vim-flavor-name") and vdu.get("vim-flavor-id"):
                             raise EngineException(
                                 "Instantiation parameters vim-flavor-name and vim-flavor-id are mutually exclusive"