Executing stored procedures in Firebird using JPA NamedStoredProcedureQuery

Question

    EntityManager em = getEntityManager();

    EntityTransaction etx = em.getTransaction();
    etx.begin();

    Query query = em.createNamedQuery("login_procedure").setParameter("param1","user").setParameter("param2", "pw");


    Integer result = 23;
    try {
        System.out.println("query = " + query.getSingleResult());
    } catch (Exception e) {
        result = null;
        e.printStackTrace();
    }

    etx.commit();
    em.close();

...executing this code I get

[EL Warning]: 2011-02-10 17:32:16.846--UnitOfWork(1267140342)--Exception [EclipseLink-4002] (Eclipse Persistence Services - 1.2.0.v20091016-r5565): org.eclipse.persistence.exceptions.DatabaseException Internal Exception: org.firebirdsql.jdbc.FBSQLException: GDS Exception. 335544569. Dynamic SQL Error SQL error code = -104 Token unknown - line 1, column 36 = Error Code: 335544569 Call: EXECUTE PROCEDURE LOGIN_PROCEDURE(USER_NAME = ?, USER_PASSWORD = ?) bind => [user, pw] Query: DataReadQuery(name="login_procedure" )

The -104 SQL error usually indicates a SQL syntax error.

Everything is processed without any error until query.getSingleResult() is called. Calling query.getResultList() doesn't change anything. I've tried several 1.x and 2.x EclipseLink versions. The Firebird DB version is 2.1.

The JPA2 declaration is:

    @Entity
@NamedStoredProcedureQuery(
        name = "login_procedure",
        resultClass = void.class,
        procedureName = "LOGIN_PROCEDURE",
        returnsResultSet = false,
        parameters = {
                @StoredProcedureParameter(queryParameter = "param1", name = "USER_NAME", direction = Direction.IN, type = String.class),
                @StoredProcedureParameter(queryParameter = "param2", name = "USER_PASSWORD", direction = Direction.IN, type = String.class)
        }
)
@Table(name = "USERS")
public class Login implements Serializable {
    @Id
    private Long id;
}

UPDATE: After tinkering a little bit more, I believe there might be an error in the EclipseLink implementation as EXECUTE PROCEDURE LOGIN_PROCEDURE(USER_NAME = ?, USER_PASSWORD = ?) isn't valid Firebird 2.1 syntax for calling procedures.