Actually this make sense, since aggregation of at table level should always return a row to represent overall picture of table, you can have count, max, avg etc. in case of no rows in table all records will simply by NULL
But in case we group data on a column, since there is no data (so there is no group element as well), it will not show any record, because nothing to group. Just imagine if one row has to be displayed with value in all aggregated column as NULL, what will be value in the grouper column, NULL? then logically you will think there is one row in the table where value of grouper is null, which will further mislead.