A day with non appointment slots causes an exception

[jamesjuett]

Current workaround is to have one random appointment slot somewhere on every day. This is definitely not sustainable in the long-term, and should be easy to fix. There's just some undefined errors to track down, and typescript should be helpful. I think the problem results from somewhere that we assume an array is non-empty and then grab the first element. This first element should be given a type that indicates it is possibly undefined.