Tidy returns empty string

Question

On my local server, this works fine. However, when I try to do this on the production server, the following returns an empty string:

$tidy = new tidy();
$tidy->repairString($html);

$html has actual HTML content before repairing (I checked), but repairString returns an empty string. Does this indicate a configuration error? Is libtidy not properly installed? How can I go about debugging this particular issue?

Thanks!

EDIT: See comments. I've found a very simple way to remove the Tidy dependency, so this question no longer needs an urgent answer. Even so, I'll leave it up for reference.