or Else
Creates and returns a new Provider that returns a fallback value if the value of this is null.
The returned provider will only be stored in a WeakReference in the parent provider (this).
Creates a new MutableProvider that returns a fallback value if the value of this is null. Conversely, if the returned provider's value is set a value equal to value, the value of this will be set to null.
The returned provider will only be stored in a WeakReference in the parent provider (this).