Note: something that might surprise you, PHP also provides a value in the $_FILES array, if the input element has no value at all, stating an error UPLOAD_ERR_NO_FILE.
So UPLOAD_ERR_NO_FILE is not an error, but a note that the input element just had no value. Thus you can't rely on the $_FILES array to see if a file was provided. Instead you have to walk the array and check every single damn entry - which can be quite difficult since the values may be nested if you use input elements named like "foo[bar][bla]".
Seems like PHP just introduced you to yet another common pitfall.
