BUG: fix size()/count() when resamping empty series (#28427)
- [X] closes #28427
- [X] tests added / passed
- [X] passes `black pandas`
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] whatsnew entry

I'm not sure this is the best way to fix this. this looked ok, can you merge master and ping on green. @jreback, For some reason, there's still one requested change (which was done). I guess github is expecting yout to validate it? > @jreback, For some reason, there's still one requested change (which was done). I guess github is expecting yout to validate it?

yes I need to still approve / re-request. @randomstuff can you merge master and ping on green. @jreback: all green. thanks @randomstuff 

sometimes these things take a while, thanks for sticking with it!

happy to have a followup to consolidate size/count across all grouping types :->