calc_nakshatra_amrta and calc_nakshatra_tyaajya not working?

[karthikraman]

import jyotisha
from jyotisha.panchaanga.spatio_temporal import City
import jyotisha.panchaanga.spatio_temporal.periodical
from jyotisha.panchaanga.temporal.nakshatra import NakshatraAssigner
city = City('Chennai', '13.08', '80.27', 'Asia/Calcutta')
panchaanga = jyotisha.panchaanga.spatio_temporal.periodical.Panchaanga(city=city, start_date='2020-04-14', end_date='2020-04-21')
nakshatra_assigner = NakshatraAssigner(panchaanga)
nakshatra_assigner.calc_nakshatra_tyaajya(False)
nakshatra_assigner.calc_nakshatra_amrta(False)

I am getting an error:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-5-4aefbf82f5d8> in <module>()
      1 nakshatra_assigner = NakshatraAssigner(panchaanga)
----> 2 nakshatra_assigner.calc_nakshatra_tyaajya(False)
      3 nakshatra_assigner.calc_nakshatra_amrta(False)

/home/karthik/GitHub/jyotisha/jyotisha/panchaanga/temporal/nakshatra.py in calc_nakshatra_tyaajya(self, debug)
     65         (n2, t_end) = (nakshatra_span.name, nakshatra_span.jd_end)
     66 
---> 67         tyaajya_start = t_start + (t_end - t_start) / 60 * (TYAJYA_SPANS_REL[n2 - 1] - 1)
     68         tyaajya_end = t_start + (t_end - t_start) / 60 * (TYAJYA_SPANS_REL[n2 - 1] + 3)
     69         self.panchaanga.tyajyam_data[d] += [(tyaajya_start, tyaajya_end)]

TypeError: unsupported operand type(s) for -: 'NoneType' and 'NoneType'

[vvasuki]

Looks like this code is not invoked by any test. Anyway, fixed a couple of typos by eyeballing.