Isset acts weird in PHP.

gotcha_isset.php

<?php

function foo($bar = NULL) {
  if (isset($bar)) {
    print "bar is set\n";
    var_dump($bar);
  }
  else {
    print "bar is not set\n";
    var_dump($bar);//If not set should throw at least a NOTICE.
  }
}

foo("hmm");
#=> bar is set
#=> string(3) "hmm"

foo();
#=> bar is not set
#=> NULL <- If it is NULL, it is set, not? *shakes head*

# On reading the documentation: isset() (http://uk.php.net/manual/en/function.isset.php) returns false for variables that _are_ set, but are  set to NULL. At least it is documented...