v2.8.0

Added

• EvaluationContext.builder() — a no-arg builder producing an anonymous context: attributes, no identity. Until now builder(userId) was the only constructor and it rejected a null id, so a context carrying attributes with no identity could not be built at all — a shape every other SDK expresses trivially. Analytics events from such a context omit userId rather than sending an empty string. (#2665)

  The workaround this replaces was actively wrong on the wire. A caller wanting an anonymous event with attributes had two spellings and both were broken: identify(null) omitted userId correctly but a null context carries no attributes, while identify(builder("").set(…)) carried the attributes but emitted "userId": "" — a present-but-empty identity, the exact shape #2397 removed from the PHP SDK. Ordinary evaluation pushed callers toward the broken one, since builder("") is how a keyless context was spelled: evaluation was always correct (an empty bucket value serves the control variation, #1457), so a caller doing the supported thing for anonymous evaluation silently emitted non-conforming events.

  builder("") is unchanged and still carries a present-but-empty identity. That is deliberate: the JS, Python, PHP and Ruby SDKs all attribute events off a null identity rather than an empty one, so an explicit "" reaches the wire in four of the five map-context SDKs; only Go drops it, and by accident of omitempty rather than by an absent-vs-empty decision. Folding "" into "absent" here would have silently changed the wire shape for existing callers to match the one SDK that never decided it.