Steps.java

import com.google.common.collect.ImmutableList;
import com.google.common.base.Optional;
import org.immutables.value.Value;

interface Step {}

@Value.Immutable
interface StepsExtends {

	ImmutableList<Step> steps();

	public class Builder extends ImmutableStepsExtends.Builder {
		public Builder addStep(Optional<Step> step) {
			if (step.isPresent()) {
				addSteps(step.get());
			}
			return this;
		}
	}
}

@Value.Immutable
interface StepsSuper {

	ImmutableList<Step> steps();

	public class Builder {
		public ImmutableStepsSuper.Builder addStep(Optional<Step> step) {
			ImmutableStepsSuper.Builder builder = (ImmutableStepsSuper.Builder) this;
			if (step.isPresent()) {
				builder.addSteps(step.get());
			}
			return builder;
		}
	}
}