xirr function returns None

[cmodi369]

Details

import datetime
from pyxirr import xirr

dates = [
    datetime.date(2020, 5, 27),
    datetime.date(2020, 5, 27),
    datetime.date(2020, 5, 27),
    datetime.date(2020, 5, 28),
    datetime.date(2020, 5, 28),
    datetime.date(2020, 5, 28),
    datetime.date(2020, 5, 28),
    datetime.date(2020, 5, 28),
    datetime.date(2020, 5, 28),
    datetime.date(2020, 5, 28)
]

values = [187.5, -30, 187.5, 187.5, 187.5, -188, -188, -188, -188, -188]

# This returns `None`
xirr(dates, values)

# Update value from -30 to -25 
values[1] = -25

# This returns `8.181769983749503e+75`
xirr(dates, values)

It would be good if instead of None exception can be raised. I am not able to understand why xirr function is returning None in the first case. Let me know how I can fix this.

Let me know your thoughts.

Thanks.