This code DOES work, however I can't make it stop adding blank UTM to the other links.

The way it should work is if there are no UTM strings set it does nothing. This snippet passes the UTM data onto other links across the site so we can use UTM paramaters across the site to trigger show/hide content.

<?php $utm_source = isset($_GET['utm_source']) ? $_GET['utm_source'] : ""; ?>
<?php $utm_medium = isset($_GET['utm_medium']) ? $_GET['utm_medium'] : ""; ?>
<?php $utm_campaign = isset($_GET['utm_campaign']) ? $_GET['utm_campaign'] : ""; ?>
<?php $utm_term = isset($_GET['utm_term']) ? $_GET['utm_term'] : ""; ?>
<?php $utm_content = isset($_GET['utm_content']) ? $_GET['utm_content'] : ""; ?>

<script type="text/javascript">
jQuery(document).ready(function ($) {
$(function() {
$("a").attr('href', function(i, h) {
return h + (h.indexOf('?') != -1 ? "&utm_source=<?php echo $utm_source; ?>&utm_medium=<?php echo $utm_medium; ?>&utm_campaign=<?php echo $utm_campaign; ?>&utm_term=<?php echo $utm_term; ?>&utm_content=<?php echo $utm_content; ?>" : "?utm_source=<?php echo $utm_source; ?>&utm_medium=<?php echo $utm_medium; ?>&utm_campaign=<?php echo $utm_campaign; ?>&utm_term=<?php echo $utm_term; ?>&utm_content=<?php echo $utm_content; ?>");
});
});
});
</script>