Throw an error if IndexModel Keys is nil

GODRIVER-456

Change-Id: I89843f6fcbfd23bffa46cef6c7abe3949ccc1c4c

Author: rfblue2

mongo/index_view.go

@@ -56,6 +56,10 @@ func (iv IndexView) CreateMany(ctx context.Context, opts []option.CreateIndexesO
 	indexes := bson.NewArray()
 
 	for _, model := range models {
+		if model.Keys == nil {
+			return nil, fmt.Errorf("index model keys cannot be nil")
+		}
+
 		name, err := getOrGenerateIndexName(model)
 		if err != nil {
 			return nil, err

mongo/index_view_internal_test.go

@@ -245,6 +245,25 @@ func TestIndexView_CreateOneWithCollationOption(t *testing.T) {
 	require.NoError(t, err)
 }
 
+func TestIndexView_CreateOneWithNilKeys(t *testing.T) {
+	t.Parallel()
+
+	if testing.Short() {
+		t.Skip()
+	}
+
+	_, coll := getIndexableCollection(t)
+	indexView := coll.Indexes()
+
+	_, err := indexView.CreateOne(
+		context.Background(),
+		IndexModel{
+			Keys: nil,
+		},
+	)
+	require.Error(t, err)
+}
+
 func TestIndexView_CreateMany(t *testing.T) {
 	t.Parallel()