Invalid argument supplied for foreach in Mage/Eav/Model/Entity/Collection/Abstract.php on line 776

Question

After upgrading magento to 1.8.1.0 (from 1.7.) I am now seeing this error in my system.log:

2014-05-26T10:39:56+00:00 ERR (3): Warning: Invalid argument supplied for foreach() in app/code/core/Mage/Eav/Model/Entity/Collection/Abstract.php on line 776

Line 776 of Abstract.php:

foreach ($fields as $alias=>$field) {
    if (isset($this->_joinFields[$alias])) {
        throw Mage::exception(
            'Mage_Eav',
            Mage::helper('eav')->__('A joint field with this alias (%s) is already declared', $alias)
        );
    }
    $this->_joinFields[$alias] = array(
        'table' => $tableAlias,
        'field' => $field,
    );
}

Anybody else seeing this error and is it a bad one or can it be ignored?