[Error] No file or variants found for asset: packages/libphonenumber_plugin/js/libphonenumber.js.

[Switernal]

I met a build error, the message said:

Error detected in `pubspec.yaml`:
No file or variants found for asset: packages/libphonenumber_plugin/js/libphonenumber.js.

I removed two lines in libphonenumber_plugin /pubspec.yaml:

    - packages/libphonenumber_plugin/js/libphonenumber.js
    - packages/libphonenumber_plugin/js/stringbuffer.js

and it worked.
I can't figure out why this happened.