replace method behaber for python3.9

change in behavior of the `replace` method in python 3.9
Before
```py
"".replace("", "p") = "p"
"".replace("", "p", 1) = ""
"".replace("", "p", 2) = ""
```

After
```py
"".replace("", "p") = "p"
"".replace("", "p", 1) = "p"
"".replace("", "p", 2) = "p"
```