Replace is_null() with === / !== NULL
Exact same behavior, but faster. I also think it's more readable.
diff --git a/system/libraries/Email.php b/system/libraries/Email.php
index 1834be2..3a38645 100644
--- a/system/libraries/Email.php
+++ b/system/libraries/Email.php
@@ -1335,7 +1335,7 @@
for ($i = 0, $c = count($this->_attachments), $z = 0; $i < $c; $i++)
{
$filename = $this->_attachments[$i]['name'][0];
- $basename = is_null($this->_attachments[$i]['name'][1])
+ $basename = $this->_attachments[$i]['name'][1] === NULL
? basename($filename) : $this->_attachments[$i]['name'][1];
$ctype = $this->_attachments[$i]['type'];
$file_content = '';