Receiving the error TypeError: Parse buffer must be String or Buffer

I've been getting the follow error in my nodejs api project. It does web scraping of a phone app web address.

C:\Program Files\GiustiziaCivileAPI-master\code\node_modules\node-expat\lib\node-expat.js:23 return this.parser.parse(buf, isFinal) ^

TypeError: Parse buffer must be String or Buffer at Parser.parse (C:\Program Files\GiustiziaCivileAPI-master\code\node_modules\node-expat\lib\node-expat.js:23:22) at Object.module.exports [as toJson] (C:\Program Files\GiustiziaCivileAPI-master\code\node_modules\xml2json\lib\xml2json.js:172:17) at ReadFileContext.callback (C:\Program Files\GiustiziaCivileAPI-master\code\setup_config\setup_config.js:33:41) at FSReqWrap.readFileAfterOpen [as oncomplete] (fs.js:237:13)

this one file that seems to be causing that

//setup_config.js
//This file is responsible for adding the user's token and UUID to the project via both method and API calling
'use strict';

var fs = require('fs');
var xmlParser = require('xml2json');

var user_uuid = "";
var user_token = "";
var user_deviceName = "";
var user_deviceWidth = "";
var user_deviceHeight = "";

//sets the user info into local file vars
async function setUserInfo(uuid, token, deviceName, deviceWidth, deviceHeight){
    if(uuid && (typeof uuid == "string")) user_uuid = uuid;
    if(token && (typeof token == "string")) user_token = token;
    if(deviceName && (typeof token == "string")) user_deviceName = deviceName;
    if(deviceWidth && (typeof token == "string")) user_deviceWidth = deviceWidth;
    if(deviceHeight && (typeof token == "string")) user_deviceHeight = deviceHeight;

    if(user_uuid && user_token && user_deviceName && user_deviceWidth && user_deviceHeight){
        //add this user info to the XML file
        return await saveUserInfoToXML();
    }
}

//try to get the user info from the persisted config XML file and send populate global vars (user_uuid, user_token)
async function retrieveUserInfoFromXML(){
    return new Promise(resolve => {
        fs.readFile('./config/config.xml', "utf8", function(err, data) {
            if(err) resolve(false);
         var jsonOfXML = JSON.parse(xmlParser.toJson(data));
         
                            
            //now populate user info into local var
            user_uuid = jsonOfXML.user_info.uuid;
            user_token = jsonOfXML.user_info.token;

            user_deviceName = jsonOfXML.user_info.deviceName;
            user_deviceWidth = jsonOfXML.user_info.deviceWidth;
            user_deviceHeight = jsonOfXML.user_info.deviceHeight;
            
            resolve(true);
         });
      });
}

//add user info on global vars to the config XML file
async function saveUserInfoToXML(){
    return new Promise(resolve => {
        var xmlFromJSON = xmlParser.toXml("{ \"user_info\": { \"token\": \""+user_token +"\", \"uuid\": \""+user_uuid +"\",  \"deviceName\": \""+user_deviceName +"\",  \"deviceWidth\": \""+user_deviceWidth +"\",  \"deviceHeight\": \""+user_deviceHeight +"\" } }");
        fs.writeFile('./config/config.xml', xmlFromJSON, function(err, data){
            if (err) resolve(false);
            resolve(true);
        });
    });
}

//get the user info inserted by the user (returns a Array containing [User ID, User Token])
function getUserInfo(){
    var errorCode = 0;
    
    if(user_uuid && (typeof user_uuid == "string") == false) errorCode +=1;
    if(user_token && (typeof user_token == "string") == false) errorCode +=1;
    
    if(user_deviceName && (typeof user_deviceName == "string") == false) errorCode +=1;
    if(user_deviceWidth && (typeof user_deviceWidth == "string") == false) errorCode +=1;
    if(user_deviceHeight && (typeof user_deviceHeight == "string") == false) errorCode +=1;

    if(errorCode == 0){
        return [user_uuid, user_token, user_deviceName, user_deviceWidth, user_deviceHeight];
    }else{
        return errorCode;
    }
}

module.exports = {
    setUserInfo, getUserInfo, retrieveUserInfoFromXML
}; 

in particular these lines> How to solve this?

if(err) resolve(false);
         var jsonOfXML = JSON.parse(xmlParser.toJson(data));
    ```

If there's an error, you are resolving the promise but then continue to run the rest of the code, which you shouldn't do (there's nothing magic to resolve that will make the rest of the code get skipped somehow).

Instead, return after resolving the promise (also in saveUserInfoToXML):

if (err) return resolve(false);
var jsonOfXML = JSON.parse(xmlParser.toJson(data));