Merge pull request #1490 from grubolsch/master

BUGFIX substr() broke when passing a NULL because of strict type

src/Monolog/Utils.php

@@ -31,7 +31,7 @@ final class Utils
             return mb_strcut($string, $start, $length);
         }
 
-        return substr($string, $start, $length);
+        return substr($string, $start, (null === $length) ? strlen($string) : $length);
     }
 
     /**