What is the potential issue with using isset() in PHP when including a file based on a variable?

The potential issue with using isset() in PHP when including a file based on a variable is that isset() only checks if a variable is set and not if it has a non-null value. This can lead to including unintended files if the variable is set but has a null value. To solve this issue, you can use the empty() function instead of isset() to check if the variable is empty before including the file.

if (!empty($variable)) {
    include $variable;
}