@Override
  protected void checkEphemeral(DfaValue left, DfaValue right) {
    if (getDfType(right) == DfTypes.NULL) {
      DfaNullability nullability = DfaNullability.fromDfType(getDfType(left));
      if (nullability == DfaNullability.UNKNOWN || nullability == DfaNullability.FLUSHED) {
        markEphemeral();
      }
    }
  }
@Override
  protected void checkEphemeral(DfaValue left, DfaValue right)