How to resolve EXTRA_KEY

private void requestHint() throws IntentSender.SendIntentException {
    HintRequest hintRequest = new HintRequest.Builder()
            .setPhoneNumberIdentifierSupported(true)
            .build();

    GoogleApiClient mGoogleApiClient = new GoogleApiClient.Builder(this)
            .build();
    PendingIntent intent = Auth.CredentialsApi.getHintPickerIntent(mGoogleApiClient , hintRequest);
    startIntentSenderForResult(intent.getIntentSender(),
            CREDENTIAL_PICKER_REQUEST, null, 0, 0, 0);
}

// Obtain the phone number from the result
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == CREDENTIAL_PICKER_REQUEST) {
        if (resultCode == RESULT_OK) {
            Credential credential = data.getParcelableExtra(Credential.EXTRA_KEY);
            textView.setText(credential.toString());
        }
    }
}