diff --git a/src/NlpTools/Tokenizers/WhitespaceTokenizer.php b/src/NlpTools/Tokenizers/WhitespaceTokenizer.php
index 8bac43c..f798bdb 100644
--- a/src/NlpTools/Tokenizers/WhitespaceTokenizer.php
+++ b/src/NlpTools/Tokenizers/WhitespaceTokenizer.php
@@ -14,6 +14,6 @@ public function tokenize($str)
     {
         $arr = array();
 
-        return preg_split(self::PATTERN,$str,null,PREG_SPLIT_NO_EMPTY);
+        return preg_split(self::PATTERN,$str,0,PREG_SPLIT_NO_EMPTY);
     }
 }