message: Add default conversion from DataSourceType<DataSourceTypeId::Nothing> to anything
diff: @@ -1556,6 +1556,18 @@ namespace value_manip {
  };
  };
  + template <>
  + struct from_value<DataSourceType<DataSourceTypeId::Nothing>> {
  + using SourceType = DataSourceType<DataSourceTypeId::Nothing>;
  +
  + template <typename DestinationType>
  + struct to_value {
  + static inline void convert(const SourceType & src, DestinationType & dest) {
  + to_null(dest);
  + }
  + };
  + };
  +
  template <>
  struct from_value<DataSourceType<DataSourceTypeId::Decimal>> {
  using SourceType = DataSourceType<DataSourceTypeId::Decimal>;
  