SQLiteQueryBuilder.query returns null cursor

I'm creating a query on the default content resolver:

Cursor cursor = resolver.query(
                            SQLiteDaoUsers.CONTENT_URI,
                            SQLiteDaoUsers.ALL_COLUMNS, null, null, null);

Where

public static final String COLUMN_ID = "_id";
public static final String COLUMN_USER_NAME = "user_name";
public static final String COLUMN_USER_BIRTH_DATE = "user_birth_date";
public static final String COLUMN_IS_DIABETES = "is_diabetes";

public static final String[] ALL_COLUMNS = {
        COLUMN_ID, COLUMN_USER_NAME, COLUMN_USER_BIRTH_DATE, COLUMN_IS_DIABETES
};

cursor is null and produces NPE, despite the fact that it should be in the worst case empty.

My ContentProvider performs query as follows:

SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
queryBuilder.setTables(SQLiteDaoUsers.TABLE_NAME);
SQLiteDatabase db = dbHelper.getWritableDatabase();
Cursor cursor = queryBuilder.query(db, projection, selection, selectionArgs,    null, null, sortOrder);
return cursor;