Formidable package treat some fields as Files - node.js

Question

I'm using to parse form/data with the formidable package, it works great but some inputs are treated as files not as fields.
Example : I send the data from the front-end with the http package in flutter like this.
var request = http.MultipartRequest('POST', postUri)
..fields['username'] = _username!
..fields['password'] = _password!
..fields['address'] = _address!
..files.add(await http.MultipartFile.fromPath(
'coverPic',
_coverImage!.path,
contentType: MediaType('image', coverPicType),
));
All fields parsed successfully instead of the address, treated as file, I don't know why ! The text inside the address was :
it's near, don't be late
The function inside Node js:
function formDataParser() {
return (req, res, next) => {
const form = formidable({});
form.parse(req, (err, fields, files) => {
console.log(fields);
console.log(files);
if (err)
return next(err);
if (!fields || !Object.keys(fields).length)
return next(err);
if (!files || !Object.keys(files).length)
return next(err);
for (var file in files) {
const image = files[file];
if (!image.originalFilename || !image.size || !image.mimetype)
return next(new Error('File specification not found');
const imageName = image.originalFilename;
const imageExt = imageName.slice(
((imageName.lastIndexOf('.') - 1) >>> 0) + 2
);
if (image.size > 10000000) {
const error = new Error('File is too large! ' + imageName);
error.originalError = 'Throwing Custom Error';
error.statusCode = 403;
return next(error);
}
if (image.mimetype !== 'image/jpeg' && image.mimetype !== 'image/png' && image.mimetype !== 'image/jpg') {
const error = new Error('File type is not allowed! ' + imageName);
error.originalError = 'Throwing Custom Error';
error.statusCode = 403;
return next(error);
}
if (imageExt !== 'jpg' && imageExt !== 'jpeg' && imageExt !== 'png') {
const error = new Error('File extension is not allowed! ' + imageName);
error.originalError = 'Throwing Custom Error';
error.statusCode = 403;
return next(error);
}
}
if (!req.body)
req.body = {};
for (field in fields) {
req.body[field] = fields[field];
}
for (file in files) {
req.body[file] = files[file];
}
return next();
});
}
}