@Nullable
    DfaValue getComparisonValue(DfaValueFactory factory) {
      if (this == NULL_VALUE || this == NOT_NULL_VALUE) return factory.fromDfType(DfTypes.NULL);
      if (this == TRUE_VALUE || this == FALSE_VALUE) return factory.fromDfType(DfTypes.TRUE);
      return null;
    }
@Nullable
    DfaValue getComparisonValue(DfaValueFactory factory)