When A Value Passed In Form Or Q'string Is Empty..

I am trying to figure out how to deal with when not all elements
in a submitted form are filled out or when page expects a query string
and doesn't get one.. I tried the two conditionals below, but still got
errors:

$param= $_GET['msg'];

/*
if ($param != "") {
echo $param;
}
*/

if (isset($param)) {
echo $param;
}

query string is:

home.php?msg=selected records have been deleted from the database.

(referrer pg is not always pg sending query string.. so need to deal
w/when no query string is passed..)