Adding users not working

public class Signup {

    public void onCreate() {
          Parse.initialize(this, "ii3MdxcmvTt6le53plXmfbPadRfEQYg0zF1GmwJH", "1XZeR6WOKoBAQYtkM1c8bGEdacQKrLEdNPonjJZC");

          username = username.trim();
          password = password.trim();
          email = email.trim();

          if(username.isEmpty() || password.isEmpty() || email.isEmpty()){
              AlertDialog.Builder builder = new AlertDialog.Builder(Signup.this);
              builder.setMessage(R.string.signup_error_message)
              .setTitle(R.string.signup_error_title)
              .setPositiveButton(android.R.string.ok, null);
        AlertDialog dialog = builder.create();    
        dialog.show();    
  }
          else{
          ParseUser user = new ParseUser();
          user.setUsername("my name");
          user.setPassword("my pass");
          user.setEmail("email@example.com");

          // other fields can be set just like with ParseObject
          user.put("phone", "650-555-0000");

          user.signUpInBackground(new SignUpCallback() {
            public void done(ParseException e) {
              if (e == null) {
                // Success
                  Intent intent = new Intent(SignUp.this, MainActivity.class);
                  intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                  intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
                  startActivity(intent);
              } 
              else {
                  AlertDialog.Builder builder = new AlertDialog.Builder(Signup.this);
                  builder.setMessage(e.getMessage())
                  .setTitle(R.string.signup_error_title)
                  .setPositiveButton(android.R.string.ok, null);
            AlertDialog dialog = builder.create();    
            dialog.show();
              }
            }
          });   

          public boolean onCreateOptionsMenu(Menu menu) {
                // Inflate the menu; this adds items to the action bar if it is present.
                getMenuInflater().inflate(R.menu.signup, menu);
                return true;
            }