refactor: change named types in nullables to structs

store/nullables.go

@@ -5,7 +5,9 @@ import (
 	"encoding/json"
 )
 
-type NullTime sql.NullTime
+type NullTime struct {
+	sql.NullTime
+}
 
 func (nt NullTime) MarshalJSON() ([]byte, error) {
 	if nt.Valid {
@@ -26,7 +28,9 @@ func (nt *NullTime) UnmarshalJSON(data []byte) error {
 	return nil
 }
 
-type NullString sql.NullString
+type NullString struct {
+	sql.NullString
+}
 
 func (ns NullString) MarshalJSON() ([]byte, error) {
 	if ns.Valid {