EclipseLink JPA 2.1 - Exception thrown when calling JPA native query and try to map the result to POJO

Question

I am using EclipseLink 2.5.2 and is using the following orm.xml to map the result of native query to POJOs.

<named-native-query name="RelSumView.findFmkItem">
    <query>
        select item_file_name
             , last_release_id
             , last_release_version
          from tableA
    </query>
</named-native-query>

<sql-result-set-mapping name="FmkItemDtoMapping">
    <constructor-result target-class="xxx.model.common.biz.dto.FmkItemDTO">
        <column name="item_file_name" class="java.lang.String" />
        <column name="last_release_id" class="java.lang.Integer" />
        <column name="last_release_version" class="java.lang.String" />
    </constructor-result>
</sql-result-set-mapping>

But in below DAO class:

public List<FmkItemDTO> getFmkReleaseItemsByEnvLabelId(int envLabelId) {
    return getEntityManager().createNamedQuery("RelSumView.findFmkItem", "FmkItemDtoMapping").getResultList();
}

The following exception is thrown:

Caused by: javax.persistence.PersistenceException: Exception [EclipseLink-6042] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.QueryException

Exception Description: A session name must be specified for non-object-level queries. See the setSessionName(String) method.

Query: ResultSetMappingQuery(sql="RelSumView.findFmkItem")
at org.eclipse.persistence.internal.jpa.QueryImpl.getResultList(QueryImpl.java:480)
at xxx.model.common.dao.FmkReleaseDAO.getFmkReleaseItemsByEnvLabelId(FmkReleaseDAO.java:28)

I have no idea of what this exception is and on how to set the session name to the query.