explode()の挙動がキモい ref: http://qiita.com/Hiraku/items/a58b8aac3f9e55cd1bd5

file0.php

var_dump(explode(' ', ''));

//array("")

file1.php

$arr = array();
$str = implode(' ', $arr);
var_dump($str); //(空文字)

$arr = explode(' ', $str);
var_dump($arr); //[''] ←ちょｗｗｗｗ

file2.php

$arr = array();
$str = implode(' ', $arr);
var_dump($str); //(空文字)

$arr = ($str==='') ? array() : explode(' ', $str);
var_dump($arr); //(空配列)