code: public static Optional<Variable> freshBuilder(SourceBuilder code, Datatype datatype) {
      if (!datatype.getBuilderFactory().isPresent()) {
        return Optional.empty();
      }
      return Optional.of(code.scope().computeIfAbsent(Declaration.FRESH_BUILDER, () -> {
        Variable defaults = new Variable("defaults");
        code.addLine("%s %s = %s;",
            datatype.getGeneratedBuilder(),
            defaults,
            datatype.getBuilderFactory().get()
                .newBuilder(datatype.getBuilder(), TypeInference.INFERRED_TYPES));
        return defaults;
      }));
    }
docs: Declares a fresh Builder to copy default property values from.
  
  <p>Reuses an existing fresh Builder instance if one was already declared in this scope.
  
  @returns a variable holding a fresh Builder, if a no-args factory method is available to
  create one with