numpy.diff返回一个空数组？

#python 3.6.3
import numpy as np

time_C0002A/1000 
array([[-0.99925  ], 
       [-0.99925  ], 
       [-0.99925  ], 
       ..., 
       [ 0.0181095], 
       [ 0.0195675], 
       [ 0.0205931]]) 

Fs_log = 1 / np.diff(time_C0002A/1000)
#python 3.6.3
import numpy as np

time_C0002A/1