One of the biggest gotchas for people new to Powershell is the handling of null, empty arrays, and single-element arrays. If you come from another language such as c# you’ll be shocked. And even for an experienced Powershell writer, the behavior can lead to ugly bugs.
Other people have covered this topic before. Here’s a good discussion by Keith Hill. But I wanted a short reference with examples of the strange (to many people) behavior, so I’m writing this today somewhat for my own benefit. But maybe someone else will find it useful.
Surrounding The Code 