Empty strings are passed to report_event func

[KostikovIlya]

I've built an example of the event_log ("example/event_log").
But it doesn't work.
Instead of
The drive C: has low free disk space. At least 2097152 Mb of free space is recommended
I've got
The drive has low free disk space. At least Mb of free space is recommended..

There is an array of empty strings in the report_event call: WORD wNumStrings = 2; const char** lpStrings = { "", ""}.
Maybe, it is related to:

 void operator() (record_view const& rec, insertion_list& insertions) const
  {
      std::size_t size = m_Formatters.size();
      insertions.resize(size);
      for (std::size_t i = 0; i < size; ++i)
      {
          typename formatter_type::stream_type strm(insertions[i]);
          m_Formatters[i](rec, strm);
          strm.flush();
      }
  }

After calling strm.flush(); insertions[i] is empty,