code: public <P extends Model> P parent(Class<P> parentClass) {
          return parent(parentClass, false);
      }
docs: Returns parent of this model, assuming that this table represents a child.
  This method may return <code>null</code> in cases when you have orphan record and
  referential integrity is not enforced in DBMS with a foreign key constraint.
  
  @param parentClass   class of a parent model.
  @return instance of a parent of this instance in the "belongs to"  relationship if found, ot null if not found.