在用np.mean时遇到了这样的bug

遇到了这样的bug

File "C:\Users\Lenovo\anaconda3\lib\site-packages\numpy\core_methods.py", line 179, in _mean
ret = umr_sum(arr, axis, dtype, out, keepdims, where=where)

TypeError: unsupported operand type(s) for +: 'NoneType' and 'NoneType'