Fatal error: Call to a member function toOptionArray() on a non-object in magento

gistfile1.php

diff --git a/app/code/core/Mage/Adminhtml/Block/System/Config/Form.php b/app/code/core/Mage/Adminhtml/Block/System/Config/Form.php
index 09fe084..b834f11 100644
--- a/app/code/core/Mage/Adminhtml/Block/System/Config/Form.php
+++ b/app/code/core/Mage/Adminhtml/Block/System/Config/Form.php
@@ -460,7 +460,11 @@ class Mage_Adminhtml_Block_System_Config_Form extends Mage_Adminhtml_Block_Widge
                             }
                         }
                     } else {
-                        $optionArray = $sourceModel->toOptionArray($fieldType == 'multiselect');
+                        if (is_object($sourceModel)) {
+                            $optionArray = $sourceModel->toOptionArray($fieldType == 'multiselect');
+                        } else {
+                            Zend_Debug::dump($element);die();
+                        }
                     }
                     $field->setValues($optionArray);
                 }