返回Object Null datasnap delphi XE2并在java Android中使用

Question

当我不想返回任何对象并在服务器上返回nil时，代理类生成了一个无法在TJSONNull TJSONObject上转换的异常..这是正常的吗？我该怎么做才能返回null或tjsonnulll？

function TServerMethods.GetPais(Codigo: Integer; var Erro:String): TPais;
var
  qry: TZQuery;
begin
  Result := nil;
  try
    qry := CreateQueryConectado(Erro);
    with qry do
    begin
      Close;
      SQL.Clear;
      SQL.Add(SQL_GET_LISTPAISES);
      SQL.Add(' WHERE pais_codigo = :P00 ');
      ParamByName('P00').AsInteger := codigo;
      Open;
      if not IsEmpty then
      begin
        Result := CreatePais;
        Result.Codigo := FieldByName('pais_codigo').AsInteger;
        Result.Nome := FieldByName('pais_descricao').AsString;
        Result.Lingua := FieldByName('pais_lingua').AsString;
        Result.Moeda := FieldByName('pais_moeda').AsString;
        Result.TaxaCambio := FieldByName('pais_taxacambio').AsCurrency;
        Result.Locale := FieldByName('pais_locale').AsString;
      end;
    end;
  except
    on e: Exception do
    begin
      Erro := TratarException(e);
    end;
  end;
end;

例如，客户的查询不存在。

这是代理类中的错误

    java.lang.ClassCastException: com.embarcadero.javaandroid.TJSONNull cannot be cast to com.embarcadero.javaandroid.TJSONObject
08-15 11:55:03.759: W/System.err(28204):  at com.embarcadero.javaandroid.DSProxy$TServerMethods.GetPais(DSProxy.java:1773)

是代理

private DSRESTParameterMetaData[] TServerMethods_GetPais_Metadata;
private DSRESTParameterMetaData[] get_TServerMethods_GetPais_Metadata() {
  if (TServerMethods_GetPais_Metadata == null) {
    TServerMethods_GetPais_Metadata = new DSRESTParameterMetaData[]{
      new DSRESTParameterMetaData("Codigo", DSRESTParamDirection.Input, DBXDataTypes.Int32Type, "Integer"),
      new DSRESTParameterMetaData("Erro", DSRESTParamDirection.InputOutput, DBXDataTypes.WideStringType, "string"),
      new DSRESTParameterMetaData("", DSRESTParamDirection.ReturnValue, DBXDataTypes.JsonValueType, "TPais"),
    };
  }
  return TServerMethods_GetPais_Metadata;
}

/**
 * @param Codigo [in] - Type on server: Integer
 * @param Erro [in/out] - Type on server: string
 * @return result - Type on server: TPais
 */
public static class GetPaisReturns {
  public String Erro;
  public TJSONObject returnValue;
}
public GetPaisReturns GetPais(int Codigo, String Erro) throws DBXException {
  DSRESTCommand cmd = getConnection().CreateCommand();
  cmd.setRequestType(DSHTTPRequestType.GET);
  cmd.setText("TServerMethods.GetPais");
  cmd.prepare(get_TServerMethods_GetPais_Metadata());
  cmd.getParameter(0).getValue().SetAsInt32(Codigo);
  cmd.getParameter(1).getValue().SetAsString(Erro);
  getConnection().execute(cmd);
  GetPaisReturns ret = new GetPaisReturns();
  ret.Erro = cmd.getParameter(1).getValue().GetAsString();
  ret.returnValue = (TJSONObject)cmd.getParameter(2).getValue().GetAsJSONValue();
  return ret;
}

坦克！