Problem getting Delphi DLL return with Java

I'm developing a system in java and a part of that system needs to get data coming from another system in Delphi.

I created two functions one that returns a String and another that returns an int . The function that returns an int works perfectly, but I'm having trouble with the function that returns a String . in Delphi it works perfectly, since when I call it in Java it gives the following error:

Exception in thread "main" java.lang.Error: Invalid memory access
at com.sun.jna.Native.invokePointer(Native Method)
at com.sun.jna.Function.invokePointer(Function.java:471)
at com.sun.jna.Function.invokeString(Function.java:652)
at com.sun.jna.Function.invoke(Function.java:396)
at com.sun.jna.Function.invoke(Function.java:316)
at com.sun.jna.Library$Handler.invoke(Library.java:232)
at com.sun.proxy.$Proxy0.testeString(Unknown Source)
at br.com.Teste.TesteDLL.main(TesteDLL.java:20)


//Classe Java que estende de StdCallLibrary
import com.sun.jna.Native;
import com.sun.jna.win32.StdCallLibrary;

public interface LeituraDLL extends StdCallLibrary {
    LeituraDLL leituraDLL = (LeituraDLL) Native.loadLibrary(
            "MinhaDLL", LeituraDLL.class);
    public int teste(int valor);
    public String testeString(String texto);    
}

// Function em Delph

library MinhaDLL;

uses
  SysUtils,
  Classes;
  {$R *.res}

function teste(v:Integer):Integer; stdcall;
  begin
    Result :=  v+5;
  end;
function testeString(v:Integer):String; stdcall;
  begin
    Result :=  'TesteString Ok';
  end;
exports teste;
exports testeString;


end.

//Chamada da Classe que estende de StdCallLibrary
import com.sun.jna.Native;

public class TesteDLL {
    public static void main(String[] args) {
        LeituraDLL leituraDLL = (LeituraDLL) Native.loadLibrary(
                "MinhaDLL", LeituraDLL.class);
        int teste = leituraDLL.teste(10);
        String testeString = leituraDLL.testeString("Ola Mundo");
        System.out.println("Retorno Function Teste: " + teste); // Retorna o valor: 15
        System.out.println("Retorno Function TesteString: " + testeString); // Exibe o erro Invalid memory access
    }

}

Has anyone ever had this problem and knows how to solve it? Note: I'm using JNA.