Handle no avatar, add delete avatar support

backend/internal/user/service.go

@@ -163,6 +163,17 @@ func (s *Service) Avatar(ctx context.Context, user *User) ([]byte, error) {
 	return s.r.Avatar(ctx, user.Id)
 }
 
+// DeleteAvatar removes a user's avatar. It is a no-op when no avatar is stored,
+// so the operation is idempotent.
+func (s *Service) DeleteAvatar(ctx context.Context, user *User) error {
+	return s.r.DeleteAvatar(ctx, user.Id)
+}
+
+// HasAvatar reports whether the user currently has an avatar stored.
+func (s *Service) HasAvatar(ctx context.Context, user *User) (bool, error) {
+	return s.r.HasAvatar(ctx, user.Id)
+}
+
 func (s *Service) ActivateUser(ctx context.Context, user *User) (*User, error) {
 	tx, err := s.r.Db.BeginTx(ctx, nil)
 	if err != nil {