An error was being returned when an empty response is expected.

When testing inequality value vars with non-matching values, the
response was sent as an error although it should return empty result
if the query has correct syntax.

Closes #2610

query/query.go

@@ -1634,7 +1634,8 @@ func (sg *SubGraph) replaceVarInFunc() error {
 
 func (sg *SubGraph) ApplyIneqFunc() error {
 	if sg.Params.uidToVal == nil {
-		return x.Errorf("Expected a valid value map. But got empty.")
+		x.Println("Expected a valid value map. But got empty.")
+		return nil
 	}
 	var typ types.TypeID
 	for _, v := range sg.Params.uidToVal {