code: public EqualsVerifierApi<T> withOnlyTheseFields(String... fields) {
          return withFieldsAddedAndValidated(allIncludedFields, Arrays.asList(fields));
      }
docs: Signals that all given fields, and <em>only</em> the given fields, are
  relevant for the {@code equals} contract. {@code EqualsVerifier} will
  fail if one of these fields does not affect the outcome of
  {@code equals}, and it will fail if a field that isn't listed here, does
  affect the outcome of {@code equals}.
  
  @param fields Fields that should be ignored.
  @return {@code this}, for easy method chaining.