NPV giving wrong results

[ajinkya976]

Hi,

For below calculations NPV is giving wrong results.

print(Finance.npv(rate: 0.05, values: <num>[1500, 2500, 3500, 4500, 6000]));

Answer through above code is : 15879.03959769849

But the correct answer is : 15122.89

[bkbonner]

Yep, you're correct. It's because the author was using index for the time period (which is zero based in his code), but needs to have 1 added to correctly calculate the NPV.

I added a pull request to add null safety and to fix the NPV calculation and tests