Runtime warning in core-shell calculation

[sampr7]

When the shell diameter becomes 114 times greater than that of wavelength, following runtime warning is arising and not calculating the extinction efficiencies and other parameters.
Input:
ps.MieQCoreShell(mCore = 1.62+0.45j, mShell=1.397+1.22e-06j, wavelength=250, dCore=2960, dShell=29600,asDict=True, asCrossSection=False)
Output:

/home/user/anaconda3/lib/python3.9/site-packages/PyMieScatt/CoreShell.py:105: RuntimeWarning: invalid value encountered in true_divide
dns = ((uufv/pw)/(uu(pw-chw*fv)+(pw/pv)/chv))+Dw