fix(opentelemetry-instrumentation-celery): detach only if the ctx tok…

…en is not None

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

@@ -215,6 +215,11 @@ def _trace_postrun(self, *args, **kwargs):
         self._record_histograms(task_id, labels)
         context_api.detach(token)
 
+        # if the process sending the task is not instrumented
+        # there's no incoming context and no token to detach
+        if token is not None:
+            context_api.detach(token)
+
     def _trace_before_publish(self, *args, **kwargs):
         task = utils.retrieve_task_from_sender(kwargs)
         task_id = utils.retrieve_task_id_from_message(kwargs)