@Nullable
  private static StandardMethodContract contractWithConstraint(ValueConstraint[] state,
                                                               int parameter, ValueConstraint paramConstraint,
                                                               ContractReturnValue returnValue) {
    ValueConstraint[] newState = withConstraint(state, parameter, paramConstraint);
    return newState == null ? null : new StandardMethodContract(newState, returnValue);
  }
@Nullable
  private static StandardMethodContract contractWithConstraint(ValueConstraint[] state,
                                                               int parameter, ValueConstraint paramConstraint,
                                                               ContractReturnValue returnValue)