How can the issue of $files[0] not being set be resolved in the given code?

The issue of $files[0] not being set can be resolved by checking if $files is not empty before trying to access its first element. This can be achieved by using the isset() function to determine if $files[0] is set before using it in the code.

if(isset($files[0])){
    // Proceed with using $files[0] as needed
    $firstFile = $files[0];
    echo "First file: " . $firstFile;
} else {
    echo "No files found.";
}