如何在pandas数据帧中绘制numpy nans的直方图

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt

df = pd.DataFrame({'A': [1, 2, np.nan, 4, 5],
                   'B': [np.nan, 2, 3, np.nan, 6]})

df.replace(np.nan, -9999, inplace=True)

plt.hist(df.values.flatten(), bins=10)
plt.xlabel('Values')
plt.ylabel('Frequency')
plt.title('Histogram of NaN Values')
plt.show()