Wrong parameter binding when using named queries with optional parameters in EclipseLink - jpa

Question

I'm trying to do a database lookup using JPA with EclipseLink. My database is Oracle 11.2.0. I have the following entity classes defined:
#Entity
#Table(name = "BS_PROVIDERS")
public class BsProvider {
#Id
#Column(name = "GUID")
private String guid;
public String getGuid() { return guid; }
public void setGuid(String guid) { this.guid = guid; }
#Column(name = "NAME")
private String name;
public String getName() { return name; }
public void setName(String name) { this.name = name; }
}
#Entity
#Table(name = "CP_PROVIDERS")
public class CpProvider{
#Id
#Column(name = "GUID")
private String guid;
public String getGuid() { return guid; }
public void setGuid(String guid) { this.guid = guid; }
#Column(name = "NAME")
private String name;
public String getName() { return name; }
public void setName(String name) { this.name = name; }
}
#NamedQueries({
#NamedQuery(
name = Catalog.FIND_BY_CPP_AND_BSP,
query = "select c from Catalog c where (c.cpProvider = :cpProvider) and ( (:bsProvider IS NULL) or (c.bsProvider = :bsProvider))"
)
})
#Entity
#Table(name = "CATALOGS")
public class Catalog {
public static final String FIND_BY_CPP_AND_BSP = "Catalog.findByCppAndBsp";
public static final String CP_PROVIDER_PARAM = "cpProvider";
public static final String BS_PROVIDER_PARAM = "bsProvider";
#Id
#Column(name = "GUID")
private String guid;
public String getGuid() { return guid; }
public void setGuid(String guid) { this.guid = guid; }
#Column(name = "NAME")
private String name;
public String getName() { return name; }
public void setName() { this.name = name; }
#ManyToOne
#JoinColumn(name = "CPP_GUID")
private CpProvider cpProvider;
public CpProvider getCpProvider() { return cpProvider; }
public void setCpProvider(CpProvider cpProvider) { this.cpProvider = cpProvider; }
#ManyToOne()
#JoinColumn(name = "BSP_GUIG")
private BsProvider bsProvider;
public BsProvider getBsProvider() { return bsProvider; }
public void setBsProvider(BsProvider bsProvider) { this.bsProvider = bsProvider; }
}
Code that creates the query and sets the parameters:
TypedQuery<Catalog> catalogQuery = em.createNamedQuery(Catalog.FIND_BY_CPP_AND_BSP, Catalog.class);
catalogQuery.setParameter(Catalog.CP_PROVIDER_PARAM, cpProvider);
catalogQuery.setParameter(Catalog.BS_PROVIDER_PARAM, bsProvider);
List<Catalog> catalogList = catalogQuery.getResultList();
When the variable bsProvider is NULL, all parameters are registerd are registerd correctly according to the EclipseLink log:
SELECT GUID, NAME, BSP_GUIG, CPP_GUID FROM CATALOGS WHERE ((CPP_GUID = ?) AND ((? IS NULL) OR (BSP_GUIG = ?)))
bind => [18EC0EDB-21A4-4845-960A-D5D2BDAC7B87, null, null]
Otherwise when the variable bsProvider refers to an existing entity I get the following exception:
Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: java.sql.SQLException: Invalid column type
Error Code: 17004
Call: SELECT GUID, NAME, BSP_GUIG, CPP_GUID FROM CATALOGS WHERE ((CPP_GUID = ?) AND ((? IS NULL) OR (BSP_GUIG = ?)))
bind => [18EC0EDB-21A4-4845-960A-D5D2BDAC7B87, com.bssys.ebpp.dbaccess.model.BsProvider#5dbbe8df, 44E8F4BF-CFDC-49DB-AB0B-718C72D6B4EF]
As you can see the first and the third parameters are bound correctly (they are replaced by the primary key values), but the second is not. What's the reason of such a strange behavior?