code: public static <T> Filter<T> bool(final boolean value) {
          return new NonMutatingFilter<T>() {
              @Override
              public boolean accepts(T item) {
                  return value;
              }
          };
      }
docs: Gets a filter that always either returns the original object unchanged
  or returns <code>null</code>.
  
  @param value whether to accept or reject all items.
  @param <T> the type.
  @return the filter.