With cftime 1.1.0 on Linux (Ubuntu, 64 bit)

I am using cftime through xarray and one my computation returns an array where the values are dates. I want to get the number of days between these dates and a reference date. Some of the pixels of the input array are masked and set to np.nan and when doing the subtraction, it raises an error TypeError: unsupported operand type(s) for -: 'float' and 'cftime._cftime_Datetime360Day.

I was wondering if there is recommended way to handle invalid values with cftime, or a plan to support this? Maybe cftime.datetime could return numpy.NaT when the other object is either numpy.nan or numpy.NaT?