fix(baggage): oversized header warn only with a header (#2212)

This commit makes sure that warnings about the baggage header length are
only emitted when the header is actually present, since it does not make
sense to warn about a missing header's length.

CHANGELOG.md

@@ -8,6 +8,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Upgrade GRPC/protobuf related dependency and regenerate otlp protobufs
   ([#2201](https://github.com/open-telemetry/opentelemetry-python/pull/2201))
+- Propagation: only warn about oversized baggage headers when headers exist
+  ([#2212](https://github.com/open-telemetry/opentelemetry-python/pull/2212))
 
 ## [1.6.0-0.25b0](https://github.com/open-telemetry/opentelemetry-python/releases/tag/v1.6.0-0.25b0) - 2021-10-13
 

opentelemetry-api/src/opentelemetry/baggage/propagation/__init__.py

@@ -53,7 +53,10 @@ def extract(
             getter.get(carrier, self._BAGGAGE_HEADER_NAME)
         )
 
-        if not header or len(header) > self._MAX_HEADER_LENGTH:
+        if not header:
+            return context
+
+        if len(header) > self._MAX_HEADER_LENGTH:
             _logger.warning(
                 "Baggage header `%s` exceeded the maximum number of bytes per baggage-string",
                 header,