ValueError: No objects to concatenate in query_physical_crossborder_allborders

[fleimgruber]

During the time interval 23:00--02:00 (UTC) the function query_physical_crossborder_allborders consistently errors with ValueError: No objects to concatenate.

The result of my analysis is that in

entsoe-py/entsoe/entsoe.py

Line 2274 in c03c604

df = pd.concat(imports, axis=1, sort=True)

imports is the empty list [] because in

entsoe-py/entsoe/entsoe.py

Lines 2270 to 2273 in c03c604

	except NoMatchingDataError:
	continue
	im.name = neighbour
	imports.append(im)

there are only NoMatchingData errors and thus imports is never appended to.

I would suggest to raise an error message that is meaningful for the user, for instance "NoMatchingData error for all neighboring crossborder flow queries" instead of letting the Pandas ValueError bubble all the way up to the user.

If you are ok with that proposal, I am going to prepare a PR.