How to add user to a role

I am trying to assign a role to a user in my signup function.

by using below code:

try {
    role.save(new CloudRoleCallback() {
    @Override
    public void done(CloudRole cloudRole, CloudException t) throws     CloudException {
        if(cloudRole != null){
            System.out.println("Adding user role"+ ""+   cloudRole.getRoleName());
            userObj.addToRole(role, new CloudUserCallback() {
                @Override
                public void done(CloudUser cloudUser, CloudException e) throws CloudException {
                    if(cloudUser != null){
                        System.out.println("role in role added successfully");
                        }
                    if(e != null){
                        e.printStackTrace();
                        }
                }
            });
        }
        if( t != null){
            t.printStackTrace();
                }
    }
});

} 
userObj.signUp(new CloudUserCallback() {
    @Override
    public void done(CloudUser cloudUser, CloudException e) throws  CloudException {
    if (cloudUser != null) {
        onSignupSuccess();
       }
    if (e != null) {
        e.printStackTrace();
        error = e.getMessage();
        error = error.substring(error.indexOf(""));
        onSignupFailed();
        progressDialog.dismiss();
        }
    }
});

When i try to run above code i am getting following error.

E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #2 Process: info, PID: 967 java.lang.RuntimeException: An error occured while executing doInBackground() at android.os.AsyncTask$3.done(AsyncTask.java:300) at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355) at java.util.concurrent.FutureTask.setException(FutureTask.java:222) at java.util.concurrent.FutureTask.run(FutureTask.java:242) at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) at java.lang.Thread.run(Thread.java:818) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference at java.io.StringReader.(StringReader.java:47) at io.cloudboost.json.JSONTokener.(JSONTokener.java:85) at io.cloudboost.json.JSONObject.(JSONObject.java:324) at io.cloudboost.CloudUser.addToRole(CloudUser.java:317) at com.rakesh_kr.msrit_info.SignUp$signupClass$1.done(SignUp.java:149) at io.cloudboost.CloudRole.save(CloudRole.java:83) at com.rakesh_kr.msrit_info.SignUp$signupClass.doInBackground(SignUp.java:144) at com.rakesh_kr.msrit_info.SignUp$signupClass.doInBackground(SignUp.java:126) at android.os.AsyncTask$2.call(AsyncTask.java:288) at java.util.concurrent.FutureTask.run(FutureTask.java:237) at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)  at java.lang.Thread.run(Thread.java:818)

@Kr Rakesh the sequence of your calls is wrong, you are essentially calling addToRole on a non existent User since you user.signUp is called later in the sequence.
What you should be doing is like so:

1. signUp
2. Create and save role in done method of signup callback
3. call addToRole inside done method of role.save callback

Below is the code I propose, so you can pick a leaf:

            user.signUp(new CloudUserCallback() {

            @Override
            public void done(final CloudUser user1, CloudException e)
                    throws CloudException {
                if (e != null)
                    e.printStackTrace();
                else {
                    CloudRole role = new CloudRole(str);
                    role.save(new CloudRoleCallback() {

                        @Override
                        public void done(CloudRole x, CloudException t)
                                throws CloudException {
                            if (t != null)
                                t.printStackTrace();
                            else {
                                user1.addToRole(x, new CloudUserCallback() {

                                    @Override
                                    public void done(CloudUser user,
                                            CloudException e)
                                            throws CloudException {
                                        if (e != null)
                                            e.printStackTrace();
                                        else {
                                            System.out
                                                .println("user added to role");
                                        }

                                    }
                            });
                        }

                    }
                });
            }

        }
    });