Refactoring validation to belong to model

internal/repository/repository_errors.go

@@ -0,0 +1,12 @@
+package repository
+
+type ErrNoOP struct{}
+type ErrEmptyUpdate struct{}
+
+func (e *ErrNoOP) Error() string {
+	return "no operation required"
+}
+
+func (e *ErrEmptyUpdate) Error() string {
+	return "update cannot be empty"
+}