NoSuchMethodError: The method 'removeRoute' was called on null.

[MalteMagnussen]

Describe the bug

NoSuchMethodError: NoSuchMethodError: The method 'removeRoute' was called on null.
Receiver: null
Tried calling: removeRoute()
  File "flushbar_route.dart", line 175, in FlushbarRoute._getDismissibleFlushbar.<fn>
  File "dismissible.dart", line 476, in _DismissibleState._startResizeAnimation
  File "dismissible.dart", line 451, in _DismissibleState._handleDismissStatusChanged
  File "<asynchronous suspension>"
  File "unparsed"

This is from our Sentry. So this happened to a user, and the above is all that Sentry has told us.
I have no clue where to start. Any help is appreciated.

Temporary solution to prevent crash