@API(status = API.Status.STABLE)
        public <T> @NonNull Builder<C> optional(
                final CommandComponent.@NonNull Builder<? super C, T> builder
        ) {
            return this.argument(builder.optional());
        }
Marks the {@code builder} as optional and adds it to the command.

@param <T> value type
@param builder the component builder
@return new builder instance with the command argument inserted into the argument list
cloud-core/src/main/java/org/incendo/cloud/Command.java