BaggageManager#getBaggage() is inconsistent when baggage doesn't exist

[adrian-skybaker]

The contract for io.micrometer.tracing.BaggageManager#getBaggage(java.lang.String) is:

@return baggage or {@code null} if not present

However, the otel implementation will create a blank (empty string) entry if not present:

    public io.micrometer.tracing.Baggage getBaggage(String name) {
        Entry entry = getBaggage(name, currentBaggage());
        return createNewEntryIfMissing(name, entry);
    }

Glancing at the code the brave implementation is sort of similar in that it also creates a baggage entry if missing, but the value looks null instead of blank string?

So it seems there are three implementations:

• (doc) return null
• (otel) return baggage with empty string value
• (brave) return baggage with null value

which is correct? The otel seems the most wrong to me, empty string looks like an actual value.

[marcingrzejszczak]

fixed via daaacab