test.php

<?php

interface BarRepository{
public function findByFoo($foo) : BarEntity[]
}

class BarRepositoryImplementation implements BarRepository{
public function findByFoo($foo): BarEntity[]
{
//Some SQL or other things 
if($noResults){ //case 1
throw new NotFoundException();
}

$collection = [new NullBarEntity()];
if($noResults){ //case 2
return $collection;
}

if($noResults){
return []; //fatal error, wrong return value
}
if($noResults){
return null; //fatal error, wrong return value
}
}
}