PHP Notice: Undefined offset: 0 in /Users/[...]ClassmapEntryFactory.php on line 27

Given this code:

$classmap = require($this->appConfig->getAppRoot() . 'vendor/composer/autoload_classmap.php');
$classmapKeys = array_keys($classmap);
return array_map(function($index) use ($classmapKeys){
    return new ClassmapEntry($classmapKeys[$index]);
}, range(0, count($classmap) - 1));

It seems like if $classmap returns an empty array, the array_map attempts to get the 0th position of $classmapKeys