fix(GraphQL): This PR fix panic error when we give null value in filter connectives. (#6707)

graphql/resolve/query_rewriter.go

@@ -1014,6 +1014,9 @@ func buildFilter(typ schema.Type, filter map[string]interface{}) *gql.FilterTree
 	// Each key in filter is either "and", "or", "not" or the field name it
 	// applies to such as "title" in: `title: { anyofterms: "GraphQL" }``
 	for _, field := range keys {
+		if filter[field] == nil {
+			continue
+		}
 		switch field {
 
 		// In 'and', 'or' and 'not' cases, filter[field] must be a map[string]interface{}

graphql/resolve/query_test.yaml

@@ -166,7 +166,21 @@
         dgraph.uid : uid
       }
     }
-
+-
+  name: "Filter connectives with null values gets skipped "
+  gqlquery: |
+    query {
+      queryAuthor(filter: { name: { eq: "A. N. Author" },not:null }) {
+        name
+      }
+    }
+  dgquery: |-
+    query {
+      queryAuthor(func: type(Author)) @filter(eq(Author.name, "A. N. Author")) {
+        name : Author.name
+        dgraph.uid : uid
+      }
+    }
 -
   name: "Filters in same input object implies AND"
   gqlquery: |