Existence check on findAncestorModel

I’ve been looking around at plugin development noticed that in cases such as the discourse translator after retrieving a widget model via findAncestorModel() there’s a check on whether the result exists before proceeding. I see this happening in the source code too, example:

  _getTopicUrl() {
    const post = this.findAncestorModel();
    return post ? post.get("topic.url") : null;

But there are also instances where we don’t check on the existence of the ancestor model, a few lines below:

      const post = this.findAncestorModel();
      const controller = this.register.lookup("controller:topic");
      return post
        .then(() => {

How reliable is the existence of the result of findAncestorModel? Does it depend on the widget we’re in, or is it good practice to always handle a null response even in situations where it seems really unlikely, like in the post-menu