Describe the bug
We have a flag with a contains rule in the email attribute. When client.variation is called the first time with key, and email, it properly evaluates whether the user should belong to that flag, and returns true if it matches. Later on the same variation call is made with the same key but with without email, and it returns false for the same flag for which true was returned when both key and email were provided.

To reproduce
Call client.variation with user.key and user.email to evaluate a flag that should resolve to true, true will be the response.
Call client.variation with the same user.key as before but without user.email, false will be the response.

Expected behavior
client.variation to identify the same user if less attributes were provided but the same key was sent.

SDK version
launchdarkly-node-server-sdk: 6.2.3

Language version, developer tools
Node v16.13.2

OS/platform
WSL2 | Ubuntu 18.04.6