Fix issue147

encode_test.go

@@ -3,6 +3,7 @@ package json_test
 import (
 	"bytes"
 	"encoding"
+	stdjson "encoding/json"
 	"errors"
 	"fmt"
 	"log"
@@ -1674,3 +1675,34 @@ func TestOmitEmpty(t *testing.T) {
 		t.Errorf(" got: %s\nwant: %s\n", got, optionalsExpected)
 	}
 }
+
+type testNullStr string
+
+func (v *testNullStr) MarshalJSON() ([]byte, error) {
+	if *v == "" {
+		return []byte("null"), nil
+	}
+
+	return []byte(*v), nil
+}
+
+func TestIssue147(t *testing.T) {
+	type T struct {
+		Field1 string      `json:"field1"`
+		Field2 testNullStr `json:"field2,omitempty"`
+	}
+	got, err := json.Marshal(T{
+		Field1: "a",
+		Field2: "b",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	expect, _ := stdjson.Marshal(T{
+		Field1: "a",
+		Field2: "b",
+	})
+	if !bytes.Equal(expect, got) {
+		t.Fatalf("expect %q but got %q", string(expect), string(got))
+	}
+}