code: def format(format)
        # Guard: fail if the passed format isn't on the whitelist
        format = format.to_s
        formatters.all.include?(format) || raise(Errors::InvalidFormatError)
  
        @format = format
        self
      end
docs: Sets the report format to a valid type
  
   @param  [#to_s] format  desired report format (one of 'array' or 'csv')
   @return [Rescuetime::Collection]
  
   TODO: make chainable to the client