code: public static AssociationAttribute<?> createEmptyAssociationAttribute(AssociationAttributeInfo info) {
  		AssociationAttribute<?> association;
  		switch (info.getType()) {
  			case MANY_TO_ONE:
  				association = new ManyToOneAttribute();
  				break;
  			case ONE_TO_MANY:
  				association = new OneToManyAttribute();
  				break;
  			default:
  				String msg = "Trying to build an unknown association attribute type " + info.getType();
  				Log.logError(msg);
  				throw new IllegalStateException(msg);
  		}
  		association.setEditable(info.isEditable());
  		return association;
  	}
docs: Creates an empty association attribute. An empty attribute is an attribute which has null as its value.
  
  @param info attribute info
  @return an empty association attribute of the right type.