x/sqlbuilder/upserter: Handle nullable DB value uniquely

x/sqlbuilder/upserter/execer.go

@@ -201,27 +201,31 @@ func newExecer(te txExecutor, stmt Statement) sqlbuilder.Execer {
 
 func cloneValue(v any) (any, error) {
 	if dv, ok := v.(driver.Valuer); ok {
-		var err error
-
-		v, err = dv.Value()
+		vv, err := dv.Value()
 
 		if err != nil {
 			return nil, err
 		}
+
+		if vv != nil {
+			v = vv
+		}
 	}
 
 	return reflect.New(reflect.TypeOf(v)).Interface(), nil
 }
 
 func equalValues(x, y any) (bool, error) {
 	if dy, ok := y.(driver.Valuer); ok {
-		var err error
-
-		y, err = dy.Value()
+		yy, err := dy.Value()
 
 		if err != nil {
 			return false, err
 		}
+
+		if yy != nil {
+			y = yy
+		}
 	}
 
 	switch yy := y.(type) {

x/sqlbuilder/upserter/upserter_test.go

@@ -104,7 +104,7 @@ func TestUpserterRegular(t *testing.T) {
 
 			res, err := e.Exec(
 				ctx,
-				map[string]interface{}{"x": "foo", "y": stringOverloaded("bar"), "z": "buz"},
+				map[string]interface{}{"x": "foo", "y": nilDBValue{}, "z": "buz"},
 			)
 
 			if err != nil {
@@ -115,7 +115,18 @@ func TestUpserterRegular(t *testing.T) {
 
 			res, err = e.Exec(
 				ctx,
-				map[string]interface{}{"x": "foo", "y": stringOverloaded("bar"), "z": "buz"},
+				map[string]interface{}{"x": "foo", "y": stringDBValue("bar"), "z": "buz"},
+			)
+
+			if err != nil {
+				t.Fatalf("Exec() = %v [ want nil ]", err)
+			}
+
+			assertResultAffected(t, res, 1)
+
+			res, err = e.Exec(
+				ctx,
+				map[string]interface{}{"x": "foo", "y": stringDBValue("bar"), "z": "buz"},
 			)
 
 			if err != nil {
@@ -449,9 +460,13 @@ func TestUpserterOnlyQueryValues(t *testing.T) {
 	})
 }
 
-type stringOverloaded string
+type nilDBValue struct{}
+
+func (nilDBValue) Value() (driver.Value, error) { return nil, nil }
+
+type stringDBValue string
 
-func (s stringOverloaded) Value() (driver.Value, error) { return []byte(s), nil }
+func (s stringDBValue) Value() (driver.Value, error) { return []byte(s), nil }
 
 func TestInTxUpserterPristine(t *testing.T) {
 	sqltest.NewTestCase(