Don't marshal empty byte or uint8 slice as null

[]byte or []uint8 are encoded as base-64 encoded string. Per this, non-nil
empty slice should not get marshalled as null, rather as "".

This restores compatibility with the standard library.

misc_tests/jsoniter_array_test.go

@@ -158,6 +158,16 @@ func Test_encode_byte_array(t *testing.T) {
 	should.Equal(`"AQID"`, string(bytes))
 }
 
+func Test_encode_empty_byte_array(t *testing.T) {
+	should := require.New(t)
+	bytes, err := json.Marshal([]byte{})
+	should.Nil(err)
+	should.Equal(`""`, string(bytes))
+	bytes, err = jsoniter.Marshal([]byte{})
+	should.Nil(err)
+	should.Equal(`""`, string(bytes))
+}
+
 func Test_decode_byte_array_from_base64(t *testing.T) {
 	should := require.New(t)
 	data := []byte{}

reflect_native.go

@@ -432,17 +432,19 @@ func (codec *base64Codec) Decode(ptr unsafe.Pointer, iter *Iterator) {
 }
 
 func (codec *base64Codec) Encode(ptr unsafe.Pointer, stream *Stream) {
-	src := *((*[]byte)(ptr))
-	if len(src) == 0 {
+	if codec.sliceType.UnsafeIsNil(ptr) {
 		stream.WriteNil()
 		return
 	}
+	src := *((*[]byte)(ptr))
 	encoding := base64.StdEncoding
 	stream.writeByte('"')
-	size := encoding.EncodedLen(len(src))
-	buf := make([]byte, size)
-	encoding.Encode(buf, src)
-	stream.buf = append(stream.buf, buf...)
+	if len(src) != 0 {
+		size := encoding.EncodedLen(len(src))
+		buf := make([]byte, size)
+		encoding.Encode(buf, src)
+		stream.buf = append(stream.buf, buf...)
+	}
 	stream.writeByte('"')
 }