Warning: array_key_exists(): The first argument should be either a string or an integer in

Warning: array_key_exists(): The first argument should be either a string or an integer in /var/www/site.com/includes/src/Df_Cms_Helper_Hierarchy.php on line 52

#0 [internal function]: mageCoreErrorHandler(2, 'array_key_exist...', '/var/www/site...', 52, Array)
#1 /var/www/site.com/includes/src/Df_Cms_Helper_Hierarchy.php(52): array_key_exists(Array, Array)
#2 /var/www/site.com/includes/src/Df_Cms_Helper_Hierarchy.php(33): Df_Cms_Helper_Hierarchy->_forcedCopyMetaData(Array, Array)
#3 /var/www/site.com/includes/src/Df_Cms_Block_Adminhtml_Cms_Hierarchy_Edit_Form.php(116): Df_Cms_Helper_Hierarchy->copyMetaData(Array, Array)
#4 /var/www/site.com/app/design/adminhtml/rm/default/template/df/cms/hierarchy/edit.phtml(32): Df_Cms_Block_Adminhtml_Cms_Hierarchy_Edit_Form->getNodesJson()
#5 /var/www/site.com/includes/src/__default.php(33033): include('/var/www/site...')
#6 /var/www/site.com/includes/src/__default.php(33064): Mage_Core_Block_Template->fetchView('adminhtml/rm/de...')
#7 /var/www/site.com/includes/src/__default.php(33078): Mage_Core_Block_Template->renderView()
#8 /var/www/site.com/includes/src/__adminhtml.php(2284): Mage_Core_Block_Template->_toHtml()
#9 /var/www/site.com/includes/src/__default.php(32324): Mage_Adminhtml_Block_Template->_toHtml()
#10 /var/www/site.com/includes/src/__default.php(32043): Mage_Core_Block_Abstract->toHtml()
#11 /var/www/site.com/includes/src/__default.php(31987): Mage_Core_Block_Abstract->_getChildHtml('form', true)
#12 /var/www/site.com/includes/src/__adminhtml.php(79724): Mage_Core_Block_Abstract->getChildHtml('form')
#13 /var/www/site.com/app/design/adminhtml/default/default/template/widget/form/container.phtml(37): Mage_Adminhtml_Block_Widget_Form_Container->getFormHtml()
#14 /var/www/site.com/includes/src/__default.php(33033): include('/var/www/site...')
#15 /var/www/site.com/includes/src/__default.php(33064): Mage_Core_Block_Template->fetchView('adminhtml/defau...')
#16 /var/www/site.com/includes/src/__default.php(33078): Mage_Core_Block_Template->renderView()
#17 /var/www/site.com/includes/src/__adminhtml.php(2284): Mage_Core_Block_Template->_toHtml()
#18 /var/www/site.com/includes/src/__adminhtml.php(79113): Mage_Adminhtml_Block_Template->_toHtml()
#19 /var/www/site.com/includes/src/__default.php(32324): Mage_Adminhtml_Block_Widget_Container->_toHtml()
#20 /var/www/site.com/includes/src/Df_Core_Block_Text_List.php(20): Mage_Core_Block_Abstract->toHtml()
#21 /var/www/site.com/includes/src/__default.php(32324): Df_Core_Block_Text_List->_toHtml()
#22 /var/www/site.com/includes/src/__default.php(32043): Mage_Core_Block_Abstract->toHtml()
#23 /var/www/site.com/includes/src/__default.php(31987): Mage_Core_Block_Abstract->_getChildHtml('content', true)
#24 /var/www/site.com/app/design/adminhtml/default/default/template/page.phtml(74): Mage_Core_Block_Abstract->getChildHtml('content')
#25 /var/www/site.com/includes/src/__default.php(33033): include('/var/www/site...')
#26 /var/www/site.com/includes/src/__default.php(33064): Mage_Core_Block_Template->fetchView('adminhtml/defau...')
#27 /var/www/site.com/includes/src/__default.php(33078): Mage_Core_Block_Template->renderView()
#28 /var/www/site.com/includes/src/__adminhtml.php(2284): Mage_Core_Block_Template->_toHtml()
#29 /var/www/site.com/includes/src/__default.php(32324): Mage_Adminhtml_Block_Template->_toHtml()
#30 /var/www/site.com/includes/src/__default.php(51846): Mage_Core_Block_Abstract->toHtml()
#31 /var/www/site.com/includes/src/__default.php(28586): Mage_Core_Model_Layout->getOutput()
#32 /var/www/site.com/app/code/local/Df/Cms/controllers/Adminhtml/Cms/HierarchyController.php(33): Mage_Core_Controller_Varien_Action->renderLayout()
#33 /var/www/site.com/includes/src/__default.php(28615): Df_Cms_Adminhtml_Cms_HierarchyController->indexAction()
#34 /var/www/site.com/includes/src/__default.php(6692): Mage_Core_Controller_Varien_Action->dispatch('index')
#35 /var/www/site.com/includes/src/__default.php(43662): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#36 /var/www/site.com/includes/src/__default.php(45261): Mage_Core_Controller_Varien_Front->dispatch()
#37 /var/www/site.com/app/Mage.php(683): Mage_Core_Model_App->run(Array)
#38 /var/www/site.com/index.php(87): Mage::run('', 'store')
#39 {main}