diff --git a/wchat/common/HttpClient.php b/wchat/common/HttpClient.php
index 5563ebe..9bf1e0a 100644
--- a/wchat/common/HttpClient.php
+++ b/wchat/common/HttpClient.php
@@ -554,7 +554,7 @@ class HttpClient
 				return $data;
 			}
 		}
-		$contentType = $this->header['Content-Type'] ?? 'application/json';
+		$contentType = $this->header['Content-Type'] ?? null;
 		if (strpos($contentType, 'json') !== false) {
 			return Help::toJson($data);
 		} else if (strpos($contentType, 'xml') !== false) {