void add(Value value)
    {
        if (values.put(value.name, value) != null)
        {
            throw err("The enum " + name + " has duplicate names: " + value.name,
                    getProto());
        }

        sortedValues.add(value);
    }
Disabled by default (the earlier protoc 2.x versions enabled this by default, but was changed later on).
protostuff-parser/src/main/java/io/protostuff/parser/EnumGroup.java