FastAPI returns 404 'detail not found' when using multiple Optional path parameters

Question

Trying to create this FastAPI app using three optional path paarameters. I tried expanding the code into three optional inputs shown below, it now forces me to input all three; otherwise, a 404 'detail not found' error is raised.

import json
from datetime import date
from typing import Optional

@app.get("/order/{country}/{menu}/{dt}")
async def ppp(country: Optional[str] = None, menu: Optional[str] = None, dt: Optional[date] = None):
    a = {}
    if country is not None:
        a["a"] = country
    else:
        return "nothing inside"
    if menu is not None:
        a["b"] = menu
    else:
        return a
    if dt is not None:
        a["c"] = dt
    return a

Expected result:

url input: http://127.0.0.1:8000/order/usa/vegan/2023-01-01

correct output: {"a":"usa","b":"vegan","c":"2023-01-01"}

However:

---

(1/3)

url input: http://127.0.0.1:8000/order/usa/vegan/

output: {"detail":"Not Found"}

expected output: {"a":"usa","b":"vegan"}

---

(2/3)

url input: http://127.0.0.1:8000/order/usa/

output: {"detail":"Not Found"}

expected output: {"a":"usa"}

---

(3/3)

url input: http://127.0.0.1:8000/order/

output: {"detail":"Not Found"}

expected output: "nothing inside"

---

All three errors shown '404 Not Found' in my uvicorn terminal