crash on MainMenu.onCreateOptionsMenu

Question

When I test my app on Xiaomi A2, it runs fine. When I upload to Google Play, it crashes. Stack Trace on Play console reads:

java.lang.NullPointerException: 
  at com.thongjoon.ocsc_exam_prep.MainMenu.onCreateOptionsMenu (MainMenu.java:29)
  at android.app.Activity.onCreatePanelMenu (Activity.java:4140)
  at androidx.fragment.app.FragmentActivity.onCreatePanelMenu (FragmentActivity.java:2) ...

This happens after I migrate to AndroidX.

Here is my onCreateOptionsMenu

public boolean onCreateOptionsMenu(Menu menu) {
        
        getMenuInflater().inflate(R.menu.menu_welcome, menu);
        MenuItem item = menu.findItem(R.id.action_share);
        mShareActionProvider = (ShareActionProvider) MenuItemCompat.getActionProvider(item);
        mShareActionProvider.setShareIntent(getDefaultShareIntent());

       String isAvailable = getApplicationContext().getResources().getString(R.string.is_show_order);

        MenuItem buyItem = menu.findItem(R.id.action_buy_sheets);
      //  if (isAvailable!=null) {
            if (!isAvailable.equals("yes")) {
                buyItem.setVisible(false);
            } else {
                buyItem.setVisible(true);
            }
    //    }

        return true;
    }

and

 @Override
    public boolean onOptionsItemSelected(MenuItem item) {
       int id = item.getItemId();
...
       if (id == R.id.action_buy_sheets) {
            startActivity(new Intent(Intent.ACTION_VIEW, 
Uri.parse("https://forms.gle/1PYvktbuGPM3MScZ9")));
            return true;
        }
...
}

in build.gradle

...
dependencies {
    implementation fileTree(include: ['*jar'], dir: 'libs')
    testImplementation 'junit:junit:4.12'
    implementation 'androidx.appcompat:appcompat:1.0.2'
    implementation 'com.google.android.material:material:1.0.0'

}
...

I use Analyze>Inspect Code to find error. No error reported. I am new. This app is my first app. Please help. Very much appreciated.