Error when i generate a converter for entity with composite pk

The problem is in the method for example:

public Object FiseUsuarioRolConverter.getAsObject(FacesContext context, UIComponent component, String value) {

if(value==null || value.length()==0){

return null;
}

FiseUsuarioRolPK id = value.toString(); --------> here is the problem (cannot convert of string to FiseUsuarioRolPK)
return FiseUsuarioRol.findFiseUsuarioRol(id);

}

I am searching solve it problem by hours. Do you have some idea ?

Jose