ImmutableList<File> inputArtifacts = subjectToTransform.getFiles();
                if (inputArtifacts.isEmpty()) {
                    return Deferrable.completed(Try.successful(subjectToTransform.createSubjectFromResult(ImmutableList.of())));
                } else if (inputArtifacts.size() > 1) {
                    return Deferrable.deferred(() ->

     */
    public abstract ComponentIdentifier getInitialComponentIdentifier();

    /**
     * Creates a subsequent subject by having transformed this subject.
     */
    public TransformStepSubject createSubjectFromResult(ImmutableList<File> result) {
        return new Transformed(this, result);
    }

    private static class Initial extends TransformStepSubject {
        private final ResolvableArtifact artifact;