What is the common mistake made in the provided PHP code snippet?

The common mistake in the provided PHP code snippet is the incorrect usage of the `isset()` function. The `isset()` function should be used to check if a variable is set and not null. In this case, the variable `$name` is being checked if it is set, but it should be checked if it is set and not empty. To fix this issue, the `empty()` function should be used instead of `isset()` to check if the variable is not empty.

// Incorrect code
if(isset($name)) {
    echo "Name is set";
} else {
    echo "Name is not set";
}

// Corrected code
if(!empty($name)) {
    echo "Name is set and not empty";
} else {
    echo "Name is either not set or empty";
}