Module gives silent White Screen of Death if PHP's DOM extension is disabled.

We recently deployed a client's website to a Voxel server. We began getting silent WSODs whenever emails were supposed to be sent. No errors were recorded to either dblog or Apache's error log.

Using the wsod module packaged with Diagnostic Tools, we were able to determine that emogrifier.php depends on the DOMDocument class, provided by the DOM PHP extension, is required:

array(4) { ["type"]=>  int(1) ["message"]=>  string(29) "Class 'DOMDocument' not found" ["file"]=>  string(74) "/var/www/html/sites/all/modules/contrib/htmlmail/emogrifier/emogrifier.php" ["line"]=>  int(78) } n/a

While DOM is enabled by default in PHP, it appears that some hosts have it disabled in the PHP packages runnin on their servers.

This dependency should probably be noted on the module page, as well as perhaps shown on admin/reports/status.