pandas replace nan multiple fields with another dataframe [duplicate]

Question

I want to replace some nan fields in the first dataframe with another dataframe. first dataframe like this:

data={'month':['2021-10','2021-11','2021-12','2022-01','2021-02'],
      'sessions':[10000,25000,32684,7415,None],
      'users':[2500,3600,4120,2154,None],
      'new_users':[750,840,980,874,680],
       'cr':[1.2,0.9,0.7,None,0.78}
df1=pd.DataFrame(data)

df1
month    sessions   users   new_users   cr
2021-10  10000      2500    750         1.2
2021-11  25000      3600    840         0.9
2021-12  32684      4120    980         0.7
2022-01  7415       2154    974         nan
2022-02  nan        nan     680         0.78

df2:

data2={'month':['2021-12','2022-01','2021-02'],
      'sessions':[32684,7415,4122],
      'users':[4120,3650,4120]
      'cr':[0.7,0.85,0.78]}
df2=pd.DataFrame(data2)

df2
month    sessions   users   cr
2021-12  32684      4120    0.7
2022-01  7415       3650    0.85
2022-02  4122       4120    0.78

expected output:

month    sessions   users   new_users  cr
2021-10  10000      2500    750        1.2
2021-11  25000      3600    840        0.9
2021-12  32684      4120    980        0.7
2022-01  7415       2154    974        0.85
2022-02  4122       4120    680        0.78