angular-file-upload module not working without selecting a file

[nani44]

I need to send form data with file and without selecting a file. whenever i select file at that time data is sending to REST API , if i am not selecting file at that time form data is not sending to REST API. It's simply throwing error file.upload undefined. How to bypass file.upload data without selecting file time

Thank you.

file.upload = Upload.upload({
url: 'MyProject/UserDetails',
data: {'user': new Blob([JSON.stringify(user)],{type: "application/json"}), 'userFiles': file},
});