GetColumnHash throws: Object reference not set to an instance of an object.

[JensBAndersen]

We are experiencing sporadic errors with the following code. We have not been able to reproduce it, but it occurs roughly once a day.

Error Message System.NullReferenceException: Object reference not set to an instance of an object. at Dapper.SqlMapper.GetColumnHash(IDataReader reader, Int32 startBound, Int32 length) in //Dapper/SqlMapper.cs:line 38 at Dapper.SqlMapper.QueryAsync[T](IDbConnection cnn, Type effectiveType, CommandDefinition command) in //Dapper/SqlMapper.Async.cs:line 420

Code

var categories = new Dictionary<Guid, Category>();

const string sql = @"
    WITH CategoryList AS
    (
        SELECT ch.Id, ch.Name, ch.ParentId
        FROM [Category] ch
        WHERE Id IN @ids

        UNION ALL

        SELECT p.Id, p.Name, p.ParentId
        FROM [Category] p 
        INNER JOIN CategoryList cl ON p.Id = cl.ParentId
    )
    SELECT DISTINCT Id, Name, ParentId FROM CategoryList";

foreach (var ids in categoriesIds.Batch(500))
{
    var result = await sqlClient.QueryAsync<Category>(sql, new { ids });

    foreach (var category in result)
    {
        categories[category.Id] = category.MapToReadModel();
    }
}

[zimaxm]

Confirm. I receive the same exception periodically