fix: None does not implement middleware when there are no middlewares (#1766)

Author: mshebeko-twist

CHANGELOG.md

@@ -22,7 +22,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fix `AttributeError` when AWS Lambda handler receives a list event
   ([#1738](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/1738))
-
+- Fix `None does not implement middleware` error when there are no middlewares registered
+  ([#1766](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/1766))
 
 ## Version 1.17.0/0.38b0 (2023-03-22)
 

instrumentation/opentelemetry-instrumentation-falcon/src/opentelemetry/instrumentation/falcon/__init__.py

@@ -245,6 +245,9 @@ def __init__(self, *args, **kwargs):
 
         # inject trace middleware
         self._middlewares_list = kwargs.pop("middleware", [])
+        if self._middlewares_list is None:
+            self._middlewares_list = []
+
         tracer_provider = otel_opts.pop("tracer_provider", None)
         meter_provider = otel_opts.pop("meter_provider", None)
         if not isinstance(self._middlewares_list, (list, tuple)):