Spring Data JPA getOne()和findOne

使用getOne()获取的是一个空的对象；用findOne则可以获取想要的；
参见源码

/**
 * Returns a reference to the entity with the given identifier.
 * 
 * @param id must not be {@literal null}.
 * @return a reference to the entity with the given identifier.
 * @see EntityManager#getReference(Class, Object)
 */
T getOne(ID id);

/**
 * Retrieves an entity by its id.
 * 
 * @param id must not be {@literal null}.
 * @return the entity with the given id or {@literal null} if none found
 * @throws IllegalArgumentException if {@code id} is {@literal null}
 */
T findOne(ID id);