Right - I attempted to add the typing but it seems I was a little overzealous when I did so by adding (string) to ListContents. I think I just misunderstood what needed the (string), so when that threw an error I backed off. Thanks for the answer!

PS: How do I add angle brackets to a comment?

D'oh. I hate getting ninja'ed. >_<

(I've deleted my reply below. It said basically the same as this, so I wasn't really adding value. Sorry about emails sent)

Instead of providing a new answer, the contents of which is a copy of the above, I'll use comments here to describe what I thought didn't make sense. ;)

It's the null-checking that doesn't make sense to me. Checking that the input argument is null implies that your code is calling this method somewhere in a fashion that risks passing null as its input, i.e. string concatenatedList = ListContents(null);

Does that ever happen anywhere in your code? There's no reason it should, so there is no reason to check if the input argument is null. You mentioned in a comment that got emailed to me that the null-checking occurs because the List is initially empty, as the player's inventory starts out empty. But as long as you've instantiated it first with the new-keyword, a List doesn't become null when empty - it's just empty. :) If the player doesn't have any items in his inventory, you can just pass in a reference to his List of items anyway, it just won't contain any items at all, and the foreach-loop will execute 0 times.

In addition, if you set the return string to null initially, but the player doesn't have any items, then this method will return the string unedited, i.e. it will return null. Does this correctly reflect an empty inventory? GUI.Label doesn't crash if it is fed a null-string, so that probably won't be an issue for you. :) But if you use the returned string elsewhere, it may throw NullReferenceExceptions later on to have it return null now. Perhaps it's safer to set the string to "" to begin with, instead of null?

So, all in all, for this method, I would just do this:

public string ListContents(List<string> iList)
{
    string invList = "";
    foreach (string item in iList)
        invList = string.Concat(invList, " ", item);        
    return invList.Trim();
}

Right, okay, that totally makes sense.

I got into the habit of checking for nulls since that's what most of my errors tend to be thus far - so the rampant null checking is pretty endemic to my code as a result.

I suppose really need to find a better coding practice, but several of my methods are often called when the input might be null, such as the above code, when I'm waiting for something to happen to trigger a method.

Elsewhere - as a newbie I don't know enough about the syntax to be anything but rather verbose, so things like not needing curly braces on one line foreach loops is news to me.

Ah, so much to learn. :p

Thanks so much for your help!