diff --git a/src/functions.php b/src/functions.php
index 1e9d044..7ec7d9f 100644
--- a/src/functions.php
+++ b/src/functions.php
@@ -91,15 +91,15 @@ function ensure_is_array($value) {
  * Get a specific configuration variable value
  *
  * @param mixed $value The value to cast
- * @param string $type The type of expected value. The configuration variable
- *                     value will be cast as this type. Could be : bool, int,
- *                     float or string.
+ * @param string|null $type The type of expected value. The configuration variable
+ *                          value will be cast as this type. Could be : bool, int,
+ *                          float or string.
  * @param bool $split If true, $type=='array' and $value is a string, split
  *                    the value by comma (optional, default: false)
  * @return mixed The cast value
  **/
 function cast($value, $type, $split=false) {
-    if (strpos($type, 'array_of_') === 0) {
+    if (is_string($type) && strpos($type, 'array_of_') === 0) {
       $type = substr($type, 9);
       $values = array();
       foreach(ensure_is_array($value) as $key => $value)