Extract getting hold of CmsSessionContext into static helper method

Object token = request.getAttribute(PREVIEW_ACCESS_TOKEN_REQUEST_ATTRIBUTE);
        if (token == null) {
            final HttpSession session = request.getSession(false);
            if (session == null) {
                return null;
            }

            return CmsSessionContext.getContext(session);
        } else {
            // token based rendering for preview
            if (token instanceof AccessToken) {
                return ((AccessToken) token).getCmsSessionContext();
            } else {
                throw new IllegalStateException(String.format("For attribute '%s' only an object of type '%s' " +
                        "is allowed", PREVIEW_ACCESS_TOKEN_REQUEST_ATTRIBUTE, AccessToken.class.getName()));
            }
        }