Prevent empty ns1 / ns2 to be used (#3683)

bin/v-change-user-ns

@@ -39,6 +39,13 @@ check_args '3' "$#" 'USER NS1 NS2 [NS3] [NS4] [NS5] [NS6] [NS7] [NS8]'
 # Checking argument format
 is_format_valid 'user' 'ns1' 'ns2'
 
+if [ "$ns1" = '' ]; then
+	check_result '3' "Usage: v-change-user-ns USER NS1 NS2 [NS3] [NS4] [NS5] [NS6] [NS7] [NS8]"
+fi
+if [ "$ns2" = '' ]; then
+	check_result '3' "Usage: v-change-user-ns USER NS1 NS2 [NS3] [NS4] [NS5] [NS6] [NS7] [NS8]"
+fi
+
 ns="$ns1,$ns2"
 if [ -n "$ns3" ]; then
 	is_format_valid 'ns3'