background_sync library Null safety

Web Background Synchronization

https://wicg.github.io/background-sync/spec/

Classes

SyncEvent
Non-standard This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future. [...]
SyncEventInit
SyncManager
The interface of the ServiceWorker API provides an interface for registering and listing sync registrations.