How to extend Entity from AbstractAuditingEntity on Jhipster generated app?

I've generated an entity with the command yo jhipster:entity MyEntity

and the following options

{
    "relationships": [],
    "fields": [
        {
            "fieldId": 1,
            "fieldName": "title",
            "fieldType": "String"
        }
    ],
    "changelogDate": "20150826154353",
    "dto": "no",
    "pagination": "no"
}

I've added the auditable columns on liquibase changelog file

<changeSet id="20150826154353" author="jhipster">
    <createSequence sequenceName="SEQ_MYENTITY" startValue="1000" incrementBy="1"/>
    <createTable tableName="MYENTITY">
        <column name="id" type="bigint" autoIncrement="${autoIncrement}" defaultValueComputed="SEQ_MYENTITY.NEXTVAL">
            <constraints primaryKey="true" nullable="false"/>
        </column>
        <column name="title" type="varchar(255)"/>

        <!--auditable columns-->
        <column name="created_by" type="varchar(50)">
            <constraints nullable="false"/>
        </column>
        <column name="created_date" type="timestamp" defaultValueDate="${now}">
            <constraints nullable="false"/>
        </column>
        <column name="last_modified_by" type="varchar(50)"/>
        <column name="last_modified_date" type="timestamp"/>
    </createTable>

</changeSet>

and modify the MyEntity class to extend AbstractAuditingEntity

@Entity
@Table(name = "MYENTITY")
@Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
public class MyEntity extends AbstractAuditingEntity implements Serializable {

then run mvn test and got the folowing exception

[DEBUG] com.example.web.rest.MyEntityResource - REST request to update MyEntity : MyEntity{id=2, title='UPDATED_TEXT'}

javax.validation.ConstraintViolationException: Validation failed for classes [com.example.domain.MyEntity] during update time for groups [javax.validation.groups.Default, ]
List of constraint violations:[
    ConstraintViolationImpl{interpolatedMessage='may not be null', propertyPath=createdBy, rootBeanClass=class com.example.domain.MyEntity, messageTemplate='{javax.validation.constraints.NotNull.message}'}
]
    at org.hibernate.cfg.beanvalidation.BeanValidationEventListener.validate(BeanValidationEventListener.java:160)
    at org.hibernate.cfg.beanvalidation.BeanValidationEventListener.onPreUpdate(BeanValidationEventListener.java:103)
    at org.hibernate.action.internal.EntityUpdateAction.preUpdate(EntityUpdateAction.java:257)
    at org.hibernate.action.internal.EntityUpdateAction.execute(EntityUpdateAction.java:134)
    at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:463)
    at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:349)
    at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:350)
    at org.hibernate.event.internal.DefaultAutoFlushEventListener.onAutoFlush(DefaultAutoFlushEventListener.java:67)
    at org.hibernate.internal.SessionImpl.autoFlushIfRequired(SessionImpl.java:1191)
    at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1257)
    at org.hibernate.internal.QueryImpl.list(QueryImpl.java:103)
    at org.hibernate.jpa.internal.QueryImpl.list(QueryImpl.java:573)
    at org.hibernate.jpa.internal.QueryImpl.getResultList(QueryImpl.java:449)
    at org.hibernate.jpa.criteria.compile.CriteriaQueryTypeQueryAdapter.getResultList(CriteriaQueryTypeQueryAdapter.java:67)
    at org.springframework.data.jpa.repository.support.SimpleJpaRepository.findAll(SimpleJpaRepository.java:318)

this is the test that's failing

@Test
    @Transactional
    public void updateMyEntity() throws Exception {
        // Initialize the database
        myEntityRepository.saveAndFlush(myEntity);

        int databaseSizeBeforeUpdate = myEntityRepository.findAll().size();

        // Update the myEntity
        myEntity.setTitle(UPDATED_TITLE);


        restMyEntityMockMvc.perform(put("/api/myEntitys")
                .contentType(TestUtil.APPLICATION_JSON_UTF8)
                .content(TestUtil.convertObjectToJsonBytes(myEntity)))
                .andExpect(status().isOk());

        // Validate the MyEntity in the database
        List<MyEntity> myEntitys = myEntityRepository.findAll();
        assertThat(myEntitys).hasSize(databaseSizeBeforeUpdate);
        MyEntity testMyEntity = myEntitys.get(myEntitys.size() - 1);
        assertThat(testMyEntity.getTitle()).isEqualTo(UPDATED_TITLE);
    }

the line that's throwing the exception is this

List<MyEntity> myEntitys = myEntityRepository.findAll();

I've noticed the TestUtil.convertObjectToJsonBytes(myEntity) method is returning the JSON object representation without the auditable properties -which is expected because of @JsonIgnore annotations- but I suppose the mockMVC.perform update operation isn't honoring the updatable = false attribute set on createdBy field

@CreatedBy
@NotNull
@Column(name = "created_by", nullable = false, length = 50, updatable = false)
@JsonIgnore
private String createdBy;

how may I make an Entity auditable and have the tests passed?