matrix addition skipping nan values

[Naveen Garg]

I would like to do element wise addition over matrices while skipping NaN values. there is nansum, but it does column wise addition within a matrix. 

let

a = NaN * zeros(3)

b = ones(3)

i want 
c = nanadd(a, b)
and 
c = b 

and 

d = nanadd(a,a)
and
d = a