BUG: Pass args and kwargs to empty

[TomAugspurger]

Closes #6952

I wasn't sure what the best way to test this was. I went with calling _apply_empty_result directly and checking for a SystemExit to get around the try: except Exception block in _apply_empty_result.

I still don't think I've 100% ensured that _apply_empty_result will always be called with _args and *_kwargs (if there are any), but if they are passed things will be handled correctly.

[TomAugspurger]

Hmm py3 failures. I can't do rase arg in py3 even if arg=ValueError. You have to wrap in an Exception(arg), which gets swallowed up by the try: except block that I'm trying to test...

suggestions?

[jreback]

not sure if it really needs a test; if it doesn't break anything else its ok

[jreback]

do you have an example that failed before? and works now?

e.g. a function on an empty frame, that could be a test

(don't have to test the generic reduction test though)

[TomAugspurger]

My tests in #6955 fail without this, so that should be good right?

[TomAugspurger]

specifically

        # test degenerate case
        q = DataFrame({'x': [], 'y': []}).quantile(0.1, axis=0)
        assert(np.isnan(q['x']) and np.isnan(q['y']))

in pandas/tests/test_frame:TestDataFrame.test_quantile

[jreback]

oh sorry..didn't see that (that's ok then)

maybe in the other PR reference the PR number just in case