{{customer.id}} is null in checkout page.

[ian_chu]

In the past, we could use {{customer.id}} to get user id in checkout page.

But somehow this liquid variable become the null recently.

The {{  customer.email }} is correct, but {{ customer.id }} is null.

I could only directly use `__st.cid,` to get userId to push DataLayer. 

And is this way correct?