code: synchronized HttpHandler getHandler(final Consumer<ServletContext> consumer) throws ServletException {
  		if (handler == null) {
  			LOG.debug("Creating handler on demand");
  			createHandler(consumer);
  		} else if (consumer != null) {
  			// Handler might be available, but the ServletContextProxy needs initialization. TODO check why
  			consumer.accept(manager.getDeployment().getServletContext());
  		}
  		return handler;
  	}
docs: Creates a new HttpHandler if not already available.
  Once the the ServletContext for this Context has been created, it will be applied to a given (optional) consumer.
  The consumer is used to update a ServletContext-OSGi-service which is actually a proxy
  @param consumer optional function to work with new ServletContext.
  @return fully initialized HttpHandler
  @throws ServletException if something goes wrong during startup
  @see ServletContextProxy