I get this error: ValueError: A value in x_new is below the interpolation range. I believe this is because the very 1st value is a nan. Anyone knows how can I get around this?

I am trying this:

y = np.array([float('nan'),2, float('nan'),4,float('nan'),5, float('nan'),float('nan'),11])

           xnew = np.arange(len(y))



           nan_idx = np.argwhere(np.isnan(y))

           xold = np.delete(xnew,nan_idx)

           yold = np.delete(y, nan_idx)



           f = interp1d(xold,yold)



           ynew = f(xnew)

 
And I get this error:
ValueError: A value in x_new is below the interpolation range.
I believe this is because the very 1st value is a nan. Anyone knows how can I get around this?
My data has nans in the very beginning and I am happy to drop that part of the data.