docs: def _timesheets_callback(self, callback):
          """
          Call a method on all the timesheets, aggregate the return values in a
          list and return it.
          """
          def call(*args, **kwargs):
              return_values = []
  
              for timesheet in self:
                  attr = getattr(timesheet, callback)
  
                  if callable(attr):
                      result = attr(*args, **kwargs)
                  else:
                      result = attr
  
                  return_values.append(result)
  
              return return_values
  
          return call