AlertDialog singleChoiceItem NullPointerException

Hi I am keep getting this exception. Below is my code. Please help me to solve this problem:

private void openDeleteCustomProfileDialog(String[] names) {

    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setTitle(R.string.delete_profile_title);
    if (names.length > 0) {
    builder.setMessage(R.string.delete_no_custom_profile);
    builder.setCancelable(false);
    builder.setSingleChoiceItems(names, -1, new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialogInterface, int which) {
            Toast.makeText(AudioFX.this, "which: " + which, Toast.LENGTH_LONG).show();
        }
    });

    builder.setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialogInterface, int which) {
            dialogInterface.dismiss();
        }
    });
    builder.setPositiveButton(R.string.delete, new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialogInterface, int which) {
            dialogInterface.dismiss();
        }
    });
    } else {
        builder.setMessage(R.string.delete_no_custom_profile);
        builder.setNegativeButton(R.string.done, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {
                dialogInterface.dismiss();
            }
        });
   }

    builder.create().show();
}