Passing empty array to date2num raises IndexError: index 0 is out of bounds for axis 0 with size 0

[roballsopp]

Environment:

cftime 1.6.2, Python 3.10.12

Description:

Passing an empty array to cftime.date2num raises the following error:

  File "src/cftime/_cftime.pyx", line 218, in cftime._cftime.date2num
IndexError: index 0 is out of bounds for axis 0 with size 0

Steps to Reproduce:

cftime.date2num([], 'seconds since 2000-01-01 12:00:00')

Expected Behavior

When passing an empty array, I expected an empty array to be returned without an error, or at least for date2num to raise a descriptive error ("an empty dates array is not supported"). The former seems to be the behavior of other functions in this package like num2pydate.

[jswhit]

closed by PR #316