code: func (c *CallService) GetNextCallsInRange(start time.Time, end time.Time, nextPageURI string) CallPageIterator {
  	if nextPageURI == "" {
  		panic("nextpageuri is empty")
  	}
  	iter := NewNextPageIterator(c.client, callsPathPart)
  	iter.SetNextPageURI(types.NullString{Valid: true, String: nextPageURI})
  	return &callDateIterator{
  		start: start,
  		end:   end,
  		p:     iter,
  	}
  }
docs: // GetNextCallsInRange retrieves the page at the nextPageURI and continues
  // retrieving pages until any results are found in the range given by start or
  // end, or we determine there are no more records to be found in that range.
  //
  // If CallPage is non-nil, it will have at least one result.