code: public static <T extends Comparable<T>> Filter<T> le(T comparable) {
          return new ComparableFilter<T>(comparable) {
              @Override
              protected boolean accepts(int result) {
                  return result <= 0;
              }
          };
      }
docs: Gets a filter that returns the original value if it is less than or
  equal to the given value, otherwise returns <code>null</code>.
  
  @param comparable the object to compare.
  @param <T> the type.
  @return the filter.