opt.fitCurve. Covariance can be "Infinity"

[NPellet]

If I copy the example

opt.fitCurve.linear([1, 2, 3, 4], [10, 3, 0, 2], function(results) {
    console.log(results);
})

I get

'float' object has no attribute 'tolist'

That's because pcov is "Infinity" (for some reason). I don't know if it's my distribution of numpy or scipy that does that, but that case should at least be handled.