自己写的一个demo，但 fulfilled 的 action.payload 拿不到值

export const fetchJokes = createAsyncThunk(
    "joke/fetchStatus",
    (num: number) => {
        axios.get(`https://autumnfish.cn/api/joke/list?num=${num}`)
            .then(res => {
                return res.data.data;
            }
    }
)
export const jokeSlice = createSlice({
    name: "joke",
    initialState: initJokeState,
    reducers: {},
    extraReducers: builder => {
        builder
            .addCase(fetchJokes.pending, (state) => {
                state.loading = true;
            })
            .addCase(fetchJokes.fulfilled, (state, action) => {
                state.loading = false;
                state.jokes = action.payload; // 这里为什么说payload是void
            })
            .addCase(fetchJokes.rejected, state => {
                state.loading = false;
            })
    }
})

请问这里action的类型是怎么决定的？