code: private void addAttributeInternal(EntityType entityType, Attribute attr) {
      if (!isPersisted(attr)) {
        return;
      }
  
      if (isMultipleReferenceType(attr)) {
        createJunctionTable(entityType, attr);
  
        if (attr.getDefaultValue() != null && !attr.isNillable()) {
          @SuppressWarnings("unchecked")
          Iterable<Entity> defaultRefEntities =
              (Iterable<Entity>) AttributeUtils.getDefaultTypedValue(attr);
          if (!Iterables.isEmpty(defaultRefEntities)) {
            createJunctionTableRows(entityType, attr, defaultRefEntities);
          }
        }
      } else {
        createColumn(entityType, attr);
      }
    }
docs: Add attribute to entityType.
  
  @param entityType the {@link EntityType} to add attribute to
  @param attr attribute to add