modify tip to avoid throwing; closes #42

[boneskull]

Modified tip and a bit of explanation to avoid throwing a TypeError. As written, it can throw an exception if called without a parameter:

> function printUpperCase(words) {
  var elements = [].concat(words);
   for (var i = 0; i < elements.length; i++) {
     console.log(elements[i].toUpperCase());
   }
 }
> printUpperCase()
TypeError:  Cannot read property 'toUpperCase' of undefined

Note that this does not avoid the exception thrown when words is neither a string nor an Array of strings.

[loverajoel]

@boneskull nice catch!

@Mattfxyz can you take a look here?

[zenopopovici]

Not sure how safe || [] is ... but in this case ...

[mattfaluotico]

This was mostly a theoretical example. It's not really code you would ever really use in production because it's such silly function. You can merge it, but I think it takes away from what the example is about.

[kurtextrem]

It makes the tip more complete. However, I would refrain from explaining that little part. A separate tip would be better I'd say (quick, but useful!)
(Example title "Logical Operators don't only compare" or so - probably something for me? :D)

[zenopopovici]

I've merged it. Thanks!

[boneskull]

ty