POST /identities incorrectly applies segment overrides when using null or empty identifier, only in Core API

[rolodato]

How are you running Flagsmith

• Self Hosted with Docker
• Self Hosted with Kubernetes
• SaaS at flagsmith.com
• Some other way (add details in description below)

Describe the bug

Consider this feature, which is disabled at the environment level but has an override for an empty segment (% Split: 0):

Calling the POST /identities endpoint on the Core API (or on any self-hosted setup) returns this flag as enabled.

Steps To Reproduce

$ curl --request POST \
  --url https://api.flagsmith.com/api/v1/identities/ \
  --header 'Accept: application/json' \
  --header 'X-Environment-Key: VmhZprhSPeaZuCeFQpKE5o' \
  --header 'content-type: application/json' \
  --data '{"identifier": ""}' | jq '.flags[] | select(.feature.name == "my_feature") | .enabled'
true

$ curl --request POST \
  --url https://edge.api.flagsmith.com/api/v1/identities/ \
  --header 'Accept: application/json' \
  --header 'X-Environment-Key: VmhZprhSPeaZuCeFQpKE5o' \
  --header 'content-type: application/json' \
  --data '{"identifier": ""}' | jq '.flags[] | select(.feature.name == "my_feature") | .enabled'
false

Expected behavior

Return the correct state of flags for blank identifiers.

Screenshots

No response