`getMaybe` to get object if registered and null otherwise

[spydon]

Sometimes you don't know if what you're looking for is already registered, it is then handy to have a get method that can return null when the registration doesn't exist.

Currently I'm using this workaround:

extension GetItExtension on GetIt {
  T? getMaybe<T extends Object>() {
    return isRegistered<T>() ? get<T>() : null;
  }
}