# scipy.spatial.distance.mahalanobis return null values for some vectors in python

I am using scipy.spatial.distance.mahalanobis to calculate distance between two vectors but i'm getting null values for some vector I don't know why? null value is possible?

Without further information, looking at the formula of Mahanologis distance. $$\sqrt{(u-v)^TV^{-1}(u-v)}$$ It is possible to obtain an error if $$V$$ is not positive definite as the input for the square root might be negative.