diff --git a/src/Rest/Client.php b/src/Rest/Client.php
index c563153..e213ff4 100644
--- a/src/Rest/Client.php
+++ b/src/Rest/Client.php
@@ -40,9 +40,12 @@ class Client extends ZuoraClientBase {
    * Perform GET request.
    *
    * @param $uri
-   * @param array|NULL $body
+   * @param null $zuora_version
+   *   The version of api to send in header.
    *
    * @return array|mixed
+   * @internal param array|NULL $body
+   *
    */
   public function get($uri, $zuora_version = null) {
     return $this->httpRequest('GET', $uri, $zuora_version);
@@ -54,6 +57,9 @@ class Client extends ZuoraClientBase {
    * @param $uri
    * @param array $body
    *
+   * @param null $zuora_version
+   *   The version of api to send in header.
+   *
    * @return array|mixed
    */
   public function post($uri, array $body, $zuora_version = null) {
@@ -66,6 +72,9 @@ class Client extends ZuoraClientBase {
    * @param $uri
    * @param array $body
    *
+   * @param null $zuora_version
+   *   The version of api to send in header.
+   *
    * @return array|mixed
    */
   public function put($uri, array $body, $zuora_version = null) {
@@ -79,9 +88,11 @@ class Client extends ZuoraClientBase {
    * @param $uri
    * @param array|NULL $body
    *
-   * @throws ZuoraException
+   * @param null $zuora_version
+   *   The version of api to send in header.
    *
    * @return array|mixed
+   * @throws \Drupal\zuora\Exception\ZuoraException
    */
   public function httpRequest($type, $uri, array $body = null, $zuora_version = null) {
     $response = $this->httpClient->request($type, '/' . self::ZUORA_API_VERSION . $uri, [
@@ -102,6 +113,9 @@ class Client extends ZuoraClientBase {
   /**
    * Returns HTTP request headers.
    *
+   * @param null $zuora_version
+   *   The version of api to send in header.
+   *
    * @return array
    */
   protected function httpHeaders($zuora_version = null) {
@@ -110,9 +124,11 @@ class Client extends ZuoraClientBase {
       'Content-Type' => 'application/json',
       'apiAccessKeyId' => $this->zuoraConfig->get('access_key_id'),
       'apiSecretAccessKey' => $this->zuoraConfig->get('access_secret_key'),
-      'zuora-version' => $zuora_version,
     ];
-    $headers = array_filter($headers);
+    if($zuora_version != NULL){
+      $headers['zuora-version'] = $zuora_version;
+    }
+    $headers = $headers;
     return $headers;
   }