diff --git a/clientv2/client.go b/clientv2/client.go
index 1b08563..d0182fc 100644
--- a/clientv2/client.go
+++ b/clientv2/client.go
@@ -396,12 +396,12 @@ func (c *Client) unmarshal(data []byte, res interface{}) error {
 
 func MarshalJSON(v interface{}) ([]byte, error) {
 	if v == nil {
-		return []byte("null"), nil // Directly return "null" for nil interface{}
+		return []byte("null"), nil
 	}
 
 	val := reflect.ValueOf(v)
 	if !val.IsValid() || (val.Kind() == reflect.Ptr && val.IsNil()) {
-		return []byte("null"), nil // Return "null" for nil pointer or invalid reflect value
+		return []byte("null"), nil
 	}
 
 	return encode(val)
@@ -417,6 +417,10 @@ func checkImplements[I any](v reflect.Value) bool {
 
 // encode returns an appropriate encoder function for the provided value.
 func encode(v reflect.Value) ([]byte, error) {
+	if !v.IsValid() || (v.Kind() == reflect.Ptr && v.IsNil()) {
+		return []byte("null"), nil
+	}
+
 	if checkImplements[graphql.Marshaler](v) {
 		return encodeGQLMarshaler(v.Interface())
 	}
@@ -457,6 +461,10 @@ func encode(v reflect.Value) ([]byte, error) {
 }
 
 func encodeGQLMarshaler(v any) ([]byte, error) {
+	if v == nil {
+		return []byte("null"), nil
+	}
+
 	var buf bytes.Buffer
 	if val, ok := v.(graphql.Marshaler); ok {
 		val.MarshalGQL(&buf)
diff --git a/clientv2/client_test.go b/clientv2/client_test.go
index 124d659..23415b9 100644
--- a/clientv2/client_test.go
+++ b/clientv2/client_test.go
@@ -579,6 +579,8 @@ func TestMarshalJSON(t *testing.T) {
 		Number Number `json:"number"`
 	}
 
+	var b *Number
+
 	// example nested struct
 	type WhereInput struct {
 		Not *WhereInput `json:"not,omitempty"`
@@ -640,6 +642,18 @@ func TestMarshalJSON(t *testing.T) {
 			},
 			want: []byte(`{"operationName":"query", "query":"query ($input: Number!) { input }","variables":{"where":{"not":{"id":"1"}}}}`),
 		},
+		{
+			name: "marshal nil",
+			args: args{
+				v: Request{
+					OperationName: "query",
+					Variables: map[string]any{
+						"v": b,
+					},
+				},
+			},
+			want: []byte(`{"operationName":"query", "query":"","variables":{"v":null}}`),
+		},
 		{
 			name: "marshal a struct with custom marshaler",
 			args: args{
@@ -738,7 +752,7 @@ func TestMarshalJSON(t *testing.T) {
 				return
 			}
 			if err := json.Unmarshal(tt.want, &wantMap); err != nil {
-				t.Errorf("Failed to unmarshal 'want': %s", tt.want)
+				t.Errorf("Failed to unmarshal err: %s", err)
 				return
 			}