@Override
  public boolean isMergeable(@NotNull DfType other) {
    if (!isSuperType(other)) return false;
    if (getNullability() == DfaNullability.UNKNOWN || getNullability() == DfaNullability.FLUSHED) {
      DfaNullability otherNullability = DfaNullability.fromDfType(other);
      return otherNullability != DfaNullability.NULL && otherNullability != DfaNullability.NULLABLE;
    }
    return true;
  }
@Override
  public boolean isMergeable(@NotNull DfType other)