Retail API predict call saves the userEvent. It should NOT!

[willapollo]

According to document, the userEvent sent as part of the predict body is not recorded.  https://cloud.google.com/retail/docs/predict#recommend

However, I noticed this was not TRUE.  Here is how to reproduce this

1. I used "FAKE_SESSION_ID_1" (literally) for making ten recommendation calls for ten skus.
2. I used "FAKE_SESSION_ID_1" to make a recommendation call for another sku ( first time) and writes down the results
3. Repeat step 2 but use "FAKE_SESSION_ID_2". The recommendation result is different from the one that uses "FAKE_SESSION_ID_1"

Because both "FAKE_SESSION_ID_1" and "FAKE_SESSION_ID_2" are never used before this experient.   The recommendation result for the same sku should be same or very similar.  But they diff a lot.