Index: date_api_filter_handler.inc
===================================================================
--- date_api_filter_handler.inc	(revision 819)
+++ date_api_filter_handler.inc	(working copy)
@@ -539,6 +539,12 @@
     else {
       $sql = $date_handler->sql_where_date('DATE', $field['fullname'], $operator, $value);
     }
+	
+	$is_null = $this->options['allow_null'] ? " OR {$field['fullname']} IS NULL" : FALSE;
+	if($is_null !== FALSE && $sql){
+		$sql .= $is_null;
+	}
+	
     return $sql;
   }