fix(datastore): adds nil check to AggregationQuery (#7376)

* fix(datastore): adds nil check to  RunAggregationQuery

datastore/query.go

@@ -627,6 +627,14 @@ func (c *Client) Run(ctx context.Context, q *Query) *Iterator {
 
 // RunAggregationQuery gets aggregation query (e.g. COUNT) results from the service.
 func (c *Client) RunAggregationQuery(ctx context.Context, aq *AggregationQuery) (AggregationResult, error) {
+	if aq == nil {
+		return nil, errors.New("datastore: aggregation query cannot be nil")
+	}
+
+	if aq.query == nil {
+		return nil, errors.New("datastore: aggregation query must include nested query")
+	}
+
 	if len(aq.aggregationQueries) == 0 {
 		return nil, errors.New("datastore: aggregation query must contain one or more operators (e.g. count)")
 	}

datastore/query_test.go

@@ -721,3 +721,33 @@ func TestAggregationQuery(t *testing.T) {
 		t.Errorf("want: %v\ngot: %v\n", want, cv)
 	}
 }
+
+func TestAggregationQueryIsNil(t *testing.T) {
+	client := &Client{
+		client: &fakeClient{
+			aggQueryFn: func(req *pb.RunAggregationQueryRequest) (*pb.RunAggregationQueryResponse, error) {
+				return fakeRunAggregationQuery(req)
+			},
+		},
+	}
+
+	var q Query
+	aq := q.NewAggregationQuery()
+	_, err := client.RunAggregationQuery(context.Background(), aq)
+	if err == nil {
+		t.Fatal(err)
+	}
+
+	q2 := NewQuery("Gopher")
+	aq2 := q2.NewAggregationQuery()
+	_, err = client.RunAggregationQuery(context.Background(), aq2)
+	if err == nil {
+		t.Fatal(err)
+	}
+
+	aq3 := q2.NewAggregationQuery().WithCount("")
+	_, err = client.RunAggregationQuery(context.Background(), aq3)
+	if err == nil {
+		t.Fatal(err)
+	}
+}