sql: correctly handle nulls in SQL type conversion

sql/type.go

@@ -302,8 +302,8 @@ func (t numberT) Type() query.Type {
 
 // SQL implements Type interface.
 func (t numberT) SQL(v interface{}) (sqltypes.Value, error) {
-	if _, ok := v.(nullT); ok {
-		return sqltypes.NULL, nil
+	if v == nil {
+		return sqltypes.MakeTrusted(t.t, nil), nil
 	}
 
 	switch t.t {
@@ -428,8 +428,8 @@ var TimestampLayouts = []string{
 
 // SQL implements Type interface.
 func (t timestampT) SQL(v interface{}) (sqltypes.Value, error) {
-	if _, ok := v.(nullT); ok {
-		return sqltypes.NULL, nil
+	if v == nil {
+		return sqltypes.MakeTrusted(sqltypes.Timestamp, nil), nil
 	}
 
 	v, err := t.Convert(v)
@@ -504,8 +504,8 @@ func (t dateT) Type() query.Type {
 }
 
 func (t dateT) SQL(v interface{}) (sqltypes.Value, error) {
-	if _, ok := v.(nullT); ok {
-		return sqltypes.NULL, nil
+	if v == nil {
+		return sqltypes.MakeTrusted(sqltypes.Timestamp, nil), nil
 	}
 
 	v, err := t.Convert(v)
@@ -561,8 +561,8 @@ func (t textT) Type() query.Type {
 
 // SQL implements Type interface.
 func (t textT) SQL(v interface{}) (sqltypes.Value, error) {
-	if _, ok := v.(nullT); ok {
-		return sqltypes.NULL, nil
+	if v == nil {
+		return sqltypes.MakeTrusted(sqltypes.Text, nil), nil
 	}
 
 	v, err := t.Convert(v)
@@ -598,8 +598,8 @@ func (t booleanT) Type() query.Type {
 
 // SQL implements Type interface.
 func (t booleanT) SQL(v interface{}) (sqltypes.Value, error) {
-	if _, ok := v.(nullT); ok {
-		return sqltypes.NULL, nil
+	if v == nil {
+		return sqltypes.MakeTrusted(sqltypes.Bit, nil), nil
 	}
 
 	b := []byte{'0'}
@@ -670,8 +670,8 @@ func (t blobT) Type() query.Type {
 
 // SQL implements Type interface.
 func (t blobT) SQL(v interface{}) (sqltypes.Value, error) {
-	if _, ok := v.(nullT); ok {
-		return sqltypes.NULL, nil
+	if v == nil {
+		return sqltypes.MakeTrusted(sqltypes.Blob, nil), nil
 	}
 
 	v, err := t.Convert(v)
@@ -714,8 +714,8 @@ func (t jsonT) Type() query.Type {
 
 // SQL implements Type interface.
 func (t jsonT) SQL(v interface{}) (sqltypes.Value, error) {
-	if _, ok := v.(nullT); ok {
-		return sqltypes.NULL, nil
+	if v == nil {
+		return sqltypes.MakeTrusted(sqltypes.TypeJSON, nil), nil
 	}
 
 	v, err := t.Convert(v)
@@ -760,10 +760,6 @@ func (t tupleT) Type() query.Type {
 }
 
 func (t tupleT) SQL(v interface{}) (sqltypes.Value, error) {
-	if _, ok := v.(nullT); ok {
-		return sqltypes.NULL, nil
-	}
-
 	return sqltypes.Value{}, fmt.Errorf("unable to convert tuple type to SQL")
 }
 
@@ -825,8 +821,8 @@ func (t arrayT) Type() query.Type {
 }
 
 func (t arrayT) SQL(v interface{}) (sqltypes.Value, error) {
-	if _, ok := v.(nullT); ok {
-		return sqltypes.NULL, nil
+	if v == nil {
+		return sqltypes.MakeTrusted(sqltypes.TypeJSON, nil), nil
 	}
 
 	v, err := t.Convert(v)

sql/type_test.go

@@ -13,7 +13,7 @@ func TestIsNull(t *testing.T) {
 	require.True(t, IsNull(nil))
 
 	n := numberT{sqltypes.Uint64}
-	require.Equal(t, sqltypes.NULL, mustSQL(n.SQL(Null)))
+	require.Equal(t, sqltypes.MakeTrusted(sqltypes.Uint64, nil), mustSQL(n.SQL(nil)))
 	require.Equal(t, sqltypes.NewUint64(0), mustSQL(n.SQL(uint64(0))))
 }