I use this code to hide attributes when they do not have data:
<?php foreach ($_additional['items'] as $_data): ?>
<?php $_attribute = $_product->getResource()->getAttribute($_data['code']);
if (!is_null($_product->getData($_attribute->getAttributeCode())) && ((string)$_attribute->getFrontend()->getValue($_product) != '')) { ?>
<tr>
<th class="label"><?php echo $this->htmlEscape($this->__($_data['label'])) ?></th>
<td class="data"><?php echo $_helper->productAttribute($_product, $_data['value'], $_data['code']) ?></td>
</tr>
<?php } ?>
<?php endforeach; ?>
This works great, but not for the type dropdown attributes.
How can I also hide dropdown attributes, that do have any value?