Fix bug if unsavedChangeValue class different with fieldValue class

Find a bug when run FCModelTest Demo.

Method `shouldInsert` and `shouldUpdate` will update time in Person Model. Call `executeUpdateQuery`, then unsavedchanges don’t include createTime and modifiedTime changes, when reload, unsavedchangess include createTime and modifiedTime changes but conflict db data, but unsavedChangeValue class is different with fieldValue class, cause an exception.