Fix panic when waiting on copied Stream notifier

[drshrey]

Description

Reference issue

Fixes #291

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.85%. Comparing base (a69c6a2) to head (18de555).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #430   +/-   ##
=======================================
  Coverage   83.84%   83.85%           
=======================================
  Files          51       51           
  Lines        3448     3449    +1     
=======================================
+ Hits         2891     2892    +1     
  Misses        417      417           
  Partials      140      140           

Flag	Coverage Δ
go	83.85% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.