fix(sqlxx): improve nulltime json unmarshal (#195)

sqlxx/types.go

@@ -97,7 +97,12 @@ func (ns *NullTime) Scan(value interface{}) error {
 
 // MarshalJSON returns m as the JSON encoding of m.
 func (ns NullTime) MarshalJSON() ([]byte, error) {
-	return json.Marshal(time.Time(ns))
+	var t *time.Time
+	if !time.Time(ns).IsZero() {
+		tt := time.Time(ns)
+		t = &tt
+	}
+	return json.Marshal(t)
 }
 
 // UnmarshalJSON sets *m to a copy of data.

sqlxx/types_test.go

@@ -0,0 +1,15 @@
+package sqlxx
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNullTime(t *testing.T) {
+	out, err := json.Marshal(NullTime{})
+	require.NoError(t, err)
+	assert.EqualValues(t, "null", string(out))
+}