diff --git a/src/Client.php b/src/Client.php
index bcaacac..671bade 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -20,19 +20,21 @@ public function __construct(ClientInterface $httpClient, ResponseBuilder $respon
      * @throws \UnexpectedValueException When response body is not a valid json
      * @throws \RuntimeException         When there are transfer errors
      */
-    public function query(string $query, array $variables = []): Response
+    public function query(string $query, array $variables = null): Response
     {
         $options = [
             'json' => [
                 'query' => $query,
-                'variables' => $variables,
             ],
         ];
+        if (!is_null($variables)) {
+            $options['json']['variables'] = $variables;
+        }
 
         try {
             $response = $this->httpClient->request('POST', '', $options);
         } catch (TransferException $e) {
-            throw new \RuntimeException('Network Error.'.$e->getMessage(), 0, $e);
+            throw new \RuntimeException('Network Error.' . $e->getMessage(), 0, $e);
         }
 
         return $this->responseBuilder->build($response);
diff --git a/tests/ClientTest.php b/tests/ClientTest.php
index bc28586..44a090a 100644
--- a/tests/ClientTest.php
+++ b/tests/ClientTest.php
@@ -70,7 +70,6 @@ public function testSimpleQueryWhenInvalidJsonIsReceived()
                 [
                     'json' => [
                         'query' => $query,
-                        'variables' => [],
                     ],
                 ]
             )
@@ -109,7 +108,6 @@ public function testSimpleQuery()
                 [
                     'json' => [
                         'query' => $query,
-                        'variables' => [],
                     ],
                 ]
             )