1545. Add changelog entry.

CHANGELOG.md

@@ -6,14 +6,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased](https://github.com/open-telemetry/opentelemetry-python/compare/v0.17b0...HEAD)
 
-=======
 ### Added
 - Added `end_on_exit` argument to `start_as_current_span`
   ([#1519](https://github.com/open-telemetry/opentelemetry-python/pull/1519)])
 - Add `Span.set_attributes` method to set multiple values with one call
   ([#1520](https://github.com/open-telemetry/opentelemetry-python/pull/1520))
 - Make sure Resources follow semantic conventions
   ([#1480](https://github.com/open-telemetry/opentelemetry-python/pull/1480))
+- Allow missing carrier headers to continue without raising AttributeError
+  ([#1545](https://github.com/open-telemetry/opentelemetry-python/pull/1545))
 
 ## [0.17b0](https://github.com/open-telemetry/opentelemetry-python/releases/tag/v0.17b0) - 2021-01-20