don't get access for database SQLite (LogCat say me that I refer at null reference)

I have main activity and fragmentList, in main class(activity) I create method methodList(he work with database) , when I click in item of my fragmentList begin work method onItemClick method of fragmentList that method turn method methodList and LogCat say me

**

Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, android.database.DatabaseErrorHandler)' on a null object reference

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ListFragment class

@Override
public void onItemClick(AdapterView<?> parent, View view, int position,long id) {
      MainActivity mainActivity = MainActivity.getInstance();
      mainActivity.methodList();

}

Main class(Activity)

public void methodList() {
    DBHelper5 dbHelper5 = new DBHelper5(getApplicationContext());
    SQLiteDatabase db = dbHelper5.getWritableDatabase();
}