code: func (out *DataOutputImpl) WriteStringSet(m map[string]bool) error {
  	if m == nil {
  		return out.WriteInt(0)
  	}
  	err := out.WriteInt(int32(len(m)))
  	if err != nil {
  		return err
  	}
  	for value, _ := range m {
  		err = out.WriteString(value)
  		if err != nil {
  			return err
  		}
  	}
  	return nil
  }
docs: /*
  Writes a String set.
  
  First the size is written as an int32, followed by each value written
  as a string.
  */