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

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();
    }
}

Inspect Dapper/SqlMapper.cs at GetColumnHash and Dapper/SqlMapper.Async.cs at QueryAsync, using the supplied NullReferenceException stack trace as the entry point. Determine which reader metadata can be null during the query path and verify the behavior with a reproducible case or regression test; done means the intermittent exception is explained and the relevant query path is covered.