public void setAttribute(Object attributeKey, Object value) throws InvalidSessionException {
        if (value == null) {
            removeAttribute(attributeKey);
        } else {
            sessionManager.setAttribute(this.key, attributeKey, value);
        }
    }
@see Session#setAttribute(Object key, Object value)
core/src/main/java/org/apache/shiro/session/mgt/DelegatingSession.java