How can I define a type in Initialstate in Redux-toolkit?

I want to define a type for the initial value in the slice state. But I don't know what to do.

If I input null in singlePost, I get this red line warning.

but I want to specify the type of the initial value of singlePost.

singlePost will contain these values.

this is my code

    // singlePost = {    //   Comments: [    //      {id: 46, content: "hello", createdAt: "2022-04-30T08:24:15.000Z",     //   }    //   {id: 47, content: "zz", createdAt: "2022-04-30T08:24:30.000Z",    // ],    // Images: [    //   PostId: 61    //   createdAt: "2022-04-27T08:17:51.000Z"    //   id: 6    //   src: "bd8b355e-cfe8-4c50-be4c-6c4958958fc6.JPEG"    //   updatedAt: "2022-04-27T08:17:51.000Z"]    //   Likecomments: [{},{}]    //   Likers: [{}]    //   User:{id:2, nickname:'elon'}    //   content:"helloword"    //   createdAt:"22022-212"    //   id: 61,    //   updatedAt:"asdasd"    // }    export const initialState = {      singlePost: null,    }    const postSlice = createSlice({      name: 'post',      initialState,      reducers: {},      extraReducers: builder =>        builder          .addCase(addComment.fulfilled, (state, action: PayloadAction<test>) => {            const post = state.mainPosts.find(v => v.id === action.payload.PostId);            state.addCommentLoading = false;            state.addCommentDone = true;            state.singlePost.Comments.push(action.payload);            post.Comments.push(action.payload);          })          .addDefaultCase(state => state),    });