Express validator – how to allow optional fields

You can use the optional method:

req.check('notexist', 'This works').optional().isInt();

This won’t work if the field is an empty string "" or false or 0 for that you need to pass in checkFalsy: true
.optional({checkFalsy: true})

An 422 status error will be thrown if you are only using .optional() & not passing any arguments.

Edit: See the docs here