code: public static void validate(OrderBy<?> orderBy,
                                  ListExpressionValidation validation,
                                  boolean ignoreUnknown) {
          if (orderBy == null) return;
          Iterator<Property> it = orderBy.getProperties().iterator();
          while (it.hasNext()) {
              validation.validate(it.next().getProperty());
              if (ignoreUnknown && !validation.lastValid()) {
                  it.remove();
              }
          }
      }
docs: <p>validate.</p>
  
  @param orderBy       a {@link io.ebean.OrderBy} object.
  @param validation    a {@link ameba.db.ebean.internal.ListExpressionValidation} object.
  @param ignoreUnknown a boolean.