Cannot upload file within FormData

Describe the bug

After upgrading from 0.24.0 to 0.25.0 File Form upload breaks.

To Reproduce

Original working on 0.24.0 code.

axios({
    method: "post",
    url: [serverUrl],
    data: formData, // FormData object instance with uploading file field
    timeout: 120000
});

This code was working previously, but now backend cannot extract file field. After specifying content type:

axios({
    method: "post",
    url: [serverUrl],
    data: formData, // FormData object instance with uploading file field
    timeout: 120000,
    headers: {"Content-Type": "multipart/form-data"},
});

I got an error on backend “bad content-type header, no multipart boundary”

Expected behavior

Seems like previous version of axios (0.24.0) automatically add correct header and also boundary. Or was there any breaking change that I didn’t notice?

Environment

• Axios Version [0.25.0]
• Node.js Version [16.0.0]
• Additional Library Versions [formidable 2.0.1, React-Native 0.66.4]

Additional context/Screenshots

Not needed.

[Romick2005]

Seems like there is a problem in isFormData function:

I am using axios in react-native project where:

const form = new FormData();
toString.call(form) === '[object Object]'; // true for React-Native
toString.call(form) === '[object FormData]'; // true for Browser
(form instanceof FormData) // true for both platforms

[tapz]

Why are these kind of useless “optimizations” even done? Why change something that works? Nobody will see any speed improvement.