diff --git a/system/libraries/Form_validation.php b/system/libraries/Form_validation.php
index 7056558..b65c488 100644
--- a/system/libraries/Form_validation.php
+++ b/system/libraries/Form_validation.php
@@ -496,7 +496,8 @@
 			return isset($array[$keys[$i]]) ? $this->_reduce_array($array[$keys[$i]], $keys, ($i+1)) : NULL;
 		}
 
-		return $array;
+		// NULL must be returned for empty fields
+		return ($array === '') ? NULL : $array;;
 	}
 
 	// --------------------------------------------------------------------