session attribute null in my spring interceptor

I am having trouble with getting a value that I had put into a session. I want to check this value with an interceptor but I only get a null.

This is where I put the variable "trustedUser"

@RequestMapping(value = "/context/{token}", method = { RequestMethod.GET })
public @ResponseBody
ResponseEntity<ContexteUI> getContextByToken(@PathVariable("token") String token, HttpSession session)
        throws ContextFault_Exception {

    HttpStatus httpStatus = HttpStatus.OK;
    if (validation(token)){
        session.setAttribute("trustedUser","trustedUser");
    } else {
        httpStatus = HttpStatus.BAD_REQUEST;
    }

    return new ResponseEntity<ContexteUI>(contexte, httpStatus);
}

This is my interceptor:

 public class AuthentificationInterceptor extends HandlerInterceptorAdapter {
    @Override
    public boolean preHandle(HttpServletRequest request,
        HttpServletResponse response, Object handler) throws Exception {

       System.out.println("Pre-handle");

       String trustedUserTest = (String) request.getSession().getAttribute("trustedUser");
       System.out.println("trustedUserTest: "+ trustedUserTest); // I only get null here, why ?

       return true;

    }
}

Where did I get wrong ?