Fix for POST calls with no request body

Author: gnongsie

generator/cybersource-javascript-template/ApiClient.mustache

@@ -526,7 +526,9 @@
     if (httpMethod.toLowerCase() === this.constants.POST
       || httpMethod.toLowerCase() === this.constants.PATCH
       || httpMethod.toLowerCase() === this.constants.PUT) {
-      bodyParam = JSON.stringify(bodyParam, null, 0);
+      if (body !== "{}") {
+        bodyParam = JSON.stringify(bodyParam, null, 0);
+      }
     }
 
     if (this.merchantConfig.getAuthenticationType().toLowerCase() !== this.constants.MUTUAL_AUTH)