Expected one result or null to be returned by selectOne but found 2

The error message indicates that the code is expecting one result or null to be returned by the selectOne() method, but instead it found two results.

This could be caused by a query that is returning more than one row of data when it should only return a single row. To fix this issue, you can modify the query or the criteria used in the selectOne() method to ensure that it only returns one result.