ok

src/Helpers/CommonHelper.php

@@ -15,7 +15,7 @@ class CommonHelper
         $signPars = "";
         ksort($params);
         foreach ($params as $k => $v) {
-            if ("" !== $v && "sign" !== $k) {
+            if ($v !== "" && $v !== null && $k !== "sign") {
                 $signPars .= $k . "=" . $v . "&";
             }
         }