CompletableTransformer

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
```
@FunctionalInterface
public interface CompletableTransformer
```
Convenience interface and callback used by the compose operator to turn a Completable into another Completable fluently.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`@NonNull CompletableSource`	`apply(@NonNull Completable upstream)`	Applies a function to the upstream `Completable` and returns a `CompletableSource`.

- Method Detail
  - apply
```
@NonNull
@NonNull CompletableSource apply(@NonNull
                                 @NonNull Completable upstream)
```
    Applies a function to the upstream Completable and returns a CompletableSource.
    
    Parameters:
    
    upstream - the upstream Completable instance
    
    Returns:
    
    the transformed CompletableSource instance