Describe the bug
According to the OpenTelemetry Baggage API Specification, baggage keys must be valid names. Empty string are not valid baggage keys and therefore should not be added to a Baggage.

Steps to reproduce

• To update ImmutableBaggage.put line 72 to add check point key.isEmpty().
• To update ImmutableBaggageTest.put_keyEmpty to ensure that empty key got skipped.

What did you expect to see?
The builder should ignore entries with empty keys, leaving the Baggage unchanged. This behavior aligns with the OpenTelemetry Baggage API Specification, which requires baggage keys to be valid names.

What did you see instead?
The builder accepts an empty string as a key and adds it to the resulting Baggage.

What version and what artifacts are you using?
Artifacts: opentelemetry-api
Version: main
How did you reference these artifacts? (excerpt from your build.gradle, pom.xml, etc)

Environment
Compiler: Temurin JDK 25
OS: Windows 11
Runtime (if different from JDK above): JDK 25
OS (if different from OS compiled on): NA

Additional context
I did refer the OpenTelemetry Baggage API Specification states that baggage keys must be valid names api.md

I'm happy to get assigned this issue to raise pr!

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