diff --git a/lib/Doctrine/Table.php b/lib/Doctrine/Table.php
index 02659b761..0842bafc8 100644
--- a/lib/Doctrine/Table.php
+++ b/lib/Doctrine/Table.php
@@ -1179,6 +1179,10 @@ public function getColumnName($fieldName)
             return $this->_columnNames[$fieldName];
         }
 
+        if (null === $fieldName) {
+            return '';
+        }
+
         return strtolower($fieldName);
     }