Runtime.getRuntime (). exec (String); does not behave the same in different equipment

I need to access the MachineGuid value of the computer's windows registry, I use this:

registryPath = "HKLM\Software\Microsoft\Cryptography";
registryKey = "MachineGuid";

Process process = Runtime.getRuntime().exec("reg query " + '"' + registryPath + "\" /v " + registryKey);

To subsequently obtain only the value of MachineGuid.

StreamReader reader = new StreamReader(process.getInputStream());
        reader.start();
        process.waitFor();
        reader.join();
        String output = reader.getResult();

        // Parse out the value
        String[] parsed = output.split(" ");              
        StringTokenizer stringMachineGuid = new StringTokenizer(parsed[parsed.length - 1]);
        String stringSinBlancos = null;
        while (stringMachineGuid.hasMoreElements()) {
            stringSinBlancos += stringMachineGuid.nextElement();
        }            
        String subString = stringSinBlancos.substring(4,stringSinBlancos.length());            
        return subString;

It's from an example that I found, in Windows 8 it works fine, but in Windows 7 it returns an empty pointer exception.

Searching the Internet I have tried the following ways:

Process process = Runtime.getRuntime().exec("reg query HKLM\Software\Microsoft\Cryptography /v MachineGuid");

Process process = Runtime.getRuntime().exec(new String []{"reg", "query", "HKLM\Software\Microsoft\Cryptography", "/v", "MachineGuid"});

String s = "reg query HKLM\Software\Microsoft\Cryptography /v MachineGuid"; Runtime.getRuntime.exec(new String [] {"bash", "-c", s});

Unsuccessful.