code: private boolean step(final Collection<Select> _selects)
      {
          boolean ret = !CollectionUtils.isEmpty(_selects);
          for (final Select select : _selects) {
              ret = ret && select.next();
          }
          return ret;
      }
docs: Move the selects to the next value.
  
  @param _selects the selects
  @return true, if successful