Fix RuntimeError: Working outside of request context. (#734)

Author: benjaminsky

CHANGELOG.md

@@ -20,7 +20,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#728](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/728))
 - `opentelemetry-propagators-aws-xray` Rename `AwsXRayFormat` to `AwsXRayPropagator`
   ([#729](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/729))
-
+- `opentelemetry-instrumentation-flask` Fix `RuntimeError: Working outside of request context`
+  ([#734](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/734))
 
 ### Changed
 - `opentelemetry-instrumentation-jinja2` Allow instrumentation of newer Jinja2 versions.

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

@@ -94,8 +94,9 @@ def _wrapped_app(wrapped_app_environ, start_response):
         wrapped_app_environ[_ENVIRON_STARTTIME_KEY] = _time_ns()
 
         def _start_response(status, response_headers, *args, **kwargs):
-            if excluded_urls is None or not excluded_urls.url_disabled(
-                flask.request.url
+            if flask.request and (
+                excluded_urls is None
+                or not excluded_urls.url_disabled(flask.request.url)
             ):
                 span = flask.request.environ.get(_ENVIRON_SPAN_KEY)