$productAttribute->getSource() is throwing an error in admin grid

The line $productAttribute->getSource() in app/code/core/Mage/Adminhtml/Block/Catalog/Product/Edit/Tab/Super/Config/Grid.php throws an error: Call to a member function getSource() on a non-object

This is the concerning function

foreach ($attributes as $attribute) { $productAttribute = $attribute->getProductAttribute(); $productAttribute->getSource(); $this->addColumn($productAttribute->getAttributeCode(), array( 'header' => $productAttribute->getFrontend()->getLabel(), 'index' => $productAttribute->getAttributeCode(), 'type' => $productAttribute->getSourceModel() ? 'options' : 'number', 'options' => $productAttribute->getSourceModel() ? $this->getOptions($attribute) : '' )); } 

I assume a certain attribute didn't get created and this is causing the issue. But how can I debug it, find out which attribute is causing the issue? I tried to var_dump $attributes and $productAttribute but that results in a blank page. Nothing in log files.

Thanks!