Room Database Query Returns Null Where It Should Be Null-safe In Kotlin

I have a query that does not have a result, when the DB is empty. Therefore NULL is the correct return value. However, the compiler in Android Studio gives me the warning: Conditio

Solution 1:

The underlying code generated by the annotation is java and thus the exception to null safety as per :-

Kotlin's type system is aimed to eliminate NullPointerException's from our code. The only possible causes of NPE's may be:

An explicit call to throw NullPointerException(); Usage of the !! operator that is described below;

Some data inconsistency with regard to initialization, such as when:

• An uninitialized this available in a constructor is passed and used somewhere ("leaking this");
• A superclass constructor calls an open member whose implementation in the derived class uses uninitialized state;
• Java interoperation:
  • Attempts to access a member on a null reference of a platform type;
  • Generic types used for Java interoperation with incorrect nullability, e.g. a piece of Java code might add null into a Kotlin MutableList, meaning that MutableList should be used for working with it;
  • Other issues caused by external Java code.

Null Safety

e.g. the generated code for queryMaxServerDate() in CourseDao would be along the lines of :-

  @Override
  public String queryMaxServerDate() {
    final String _sql = "SELECT max(last_mopdified) from course";
    final RoomSQLiteQuery _statement = RoomSQLiteQuery.acquire(_sql, 0);
    __db.assertNotSuspendingTransaction();
    final Cursor _cursor = DBUtil.query(__db, _statement, false, null);
    try {
      final String _result;
      if(_cursor.moveToFirst()) {
        final String _tmp;
        _tmp = _cursor.getString(0);
        _result = _tmp;
      } else {
        _result = null;
      }
      return _result;
    } finally {
      _cursor.close();
      _statement.release();
    }
  }

As you can see, no data extracted (no first row) and null is returned.