NaN runtime warnings

[dusvyat]

/python3.9/site-packages/numpy/core/fromnumeric.py:3474: RuntimeWarning: Mean of empty slice.
return _methods._mean(a, axis=axis, dtype=dtype,

/python3.9/site-packages/numpy/core/_methods.py:189: RuntimeWarning: invalid value encountered in double_scalars
ret = ret.dtype.type(ret / rcount)