code: private boolean matches(String filter, String value) {
          if (filter == null) {
              return true;
          }
          return filter.equals(value);
      }
docs: Checks whether the string filter matches the provided value.
  <p>
  Filter can be null, which means "match all".
  @param filter string filter
  @param value value to match against
  @return true if the filter matches the value, otherwise false