How to specify the image type in typescript?

Question

How to specify the fileSelect's type in typescript ? I'm refactoring my code to typescript but there is Error in useState and formData.append("file", fileSelect)'s type error

so this is part of my code and

const [fileSelect, setFileSelect] = useState<File | null>(null);

this has type error

import React from "react";
import wellcome from "../char-image/welcome.png";
import chat from "../char-image/chat.png";
import { useState, useRef, useEffect } from "react";
import UserAndBlock from "./UserAndBlock";
import { messageType } from '../App'
import { eType } from '../App'
import { blockListType } from '../App'
import { chatingPageProps } from '../page/ChatingPage'

let getImage: File | null = null;
let chatTyping: boolean = false;
function Chatroom({
  ws,
  fetchChatList,
  isUserName,
  isUserId,
  onChat,
  setOnchat,
  openUserList,
  typingM,
  leaveChat,
  openHandler,
  enterMsg,
  setOpenUserList,
  blockList,
  setBlockList,
  setWs,
}: chatingPageProps) {
  const messageRef = useRef<HTMLDivElement>(null);
  const [fileSelect, setFileSelect] = useState<File | null>(null); 
  const [isFile, setIsFile] = useState<boolean>(false);
  const [fileSend, setFileSend] = useState<boolean>(false); 
  const [sendMessage, setSendMessage] = useState<string>(""); 
  const [isUserList, setIsUserList] = useState<messageType[]>([]); 
  const filterdMessage = enterMsg.filter((msg: messageType) => {
    return !blockList.some((bl: blockListType) => {
      return msg.idx === bl.target;
    });
  });
  const cancelImage = () => {
    getImage = null;
    setIsFile(false);
    setFileSend(false);
  };
  const handlePost = async () => {
    const formData = new FormData();
    formData.append("file", fileSelect);
    return fetch(`http://localhost:8443/upload?file=${isFile}`, {
      method: "POST",
      body: formData,
      headers: {
        "Content-Type": "multipart/form-data",
      },
    })
      .then((res) => res.json())
      .then((res) => {
        getImage = res;
        sendImage();
      });
  };
  const sendImage = () => {
    if (getImage) {
      ws.send(
        JSON.stringify({
          event: "message",
          message: getImage.upload,
        })
      );
    }
    ws.onmessage = function () {
      fetchChatList();
    };
    scrollToBottom();
    setFileSelect(null);
    setIsFile(false);
    setFileSend(false);
  };

this code to upload file but I dont know what type is that

  const [fileSelect, setFileSelect] = useState<File | null>(null); 

const handlePost = async () => {
    const formData = new FormData();
    formData.append("file", fileSelect);// fileSelect has error 
                                        //"Argument of type 'File | null' is not 
                                   //   assignable to parameter of type 'string | Blob'.
                                // Type 'null' is not assignable to type 'string | Blob'"
    return fetch(`http://localhost:8443/upload?file=${isFile}`, {
      method: "POST",
      body: formData,
      headers: {
        "Content-Type": "multipart/form-data",
      },
    })
      .then((res) => res.json())
      .then((res) => {
        getImage = res;
        sendImage();
      });
  };