Fixes bug related to new version of yq

Change-Id: Ia4d7cad2dea93ad61dab6893342a885140138c8e
Signed-off-by: aguilarherna <daguilarh@indra.es>
diff --git a/robot-systest/lib/ns_lib.robot b/robot-systest/lib/ns_lib.robot
index bc92910..ed6e699 100644
--- a/robot-systest/lib/ns_lib.robot
+++ b/robot-systest/lib/ns_lib.robot
@@ -267,5 +267,6 @@
 
     ${rc}  ${stdout}=  Run and Return RC and Output  osm vnf-show ${vnf_id} --kdu ${kdu_name} | yq .config.replicaCount | tr -d \\"
     Should Be Equal As Integers  ${rc}  ${success_return_code}  msg=${stdout}  values=False
-    [Return]  ${stdout}
+    ${return} =   Set Variable If   '${stdout}' == 'null'   ${EMPTY}    ${stdout}
+    [Return]  ${return}