public Session session(boolean create) {
        if (session == null || !validSession) {
            HttpSession httpSession = servletRequest.getSession(create);
            if (httpSession != null) {
                validSession(true);
                session = new Session(httpSession, this);
            } else {
                session = null;
            }
        }
        return session;
    }
Returns the current session associated with this request, or if there is
no current session and <code>create</code> is true, returns  a new session.

@param create <code>true</code> to create a new session for this request if necessary;
              <code>false</code> to return null if there's no current session
@return the session associated with this request or <code>null</code> if
<code>create</code> is <code>false</code> and the request has no valid session
src/main/java/spark/Request.java