public ClientConfig setUserContext(ConcurrentMap<String, Object> userContext) {
        isNotNull(userContext, "userContext");
        this.userContext.clear();
        this.userContext.putAll(userContext);
        return this;
    }
@Test(expected = IllegalArgumentException.class)
    public void testUserContext_throwExceptionWhenContextNull() {
        ClientConfig clientConfig = new ClientConfig();
        clientConfig.setUserContext(null);
    }