JAVA: Solution to "appengine-web.xml does not contain a element"

I'm trying to run the CodeLabEx of the Google App Engine tutorial.
Importing the starter project to Eclipse I've this error:

SEVERE: Received exception processing C:\User\Eclipse\workspace\CodeLabEx\war\WEB-INF/appengine-web.xmlcom.google.apphosting.utils.config.AppEngineConfigException: appengine-web.xml does not contain a <threadsafe> element.See http://code.google.com/appengine/docs/java/config/appconfig.html#Using_Concurrent_Requests for more information.You probably want to enable concurrent requests.

I find the solution.
Simply add <threadsafe>true</threadsafe> to your war/WEB-INF/appengine-web.xml:
Something like this:

<?xml version="1.0" encoding="UTF-8"?><appengine-web-app xmlns="http://appengine.google.com/ns/1.0"><application></application><version>1</version><threadsafe>true</threadsafe>

Error description: 
http://code.google.com/appengine/docs/java/config/appconfig.html#Using_Concurrent_Requests