Which of the following code blocks returns a new DataFrame where column managerName from DataFrame storesDF has had its null values replaced with the string "No Manager"?

A sample of DataFrame storesDF is below:

storeId  managerName
0        Donec Enim
1        Ultrices Fringilla
2        null
3        Magna Ac
4        null

storeId  managerName
0        Donec Enim
1        Ultrices Fringilla
2        null
3        Magna Ac
4        null