This error may occur if some of your jar files are not compiled. You must enter your build.gradle file in your project and look in your dependencies.
If you just import some jar files, you can try to delete them and add them one at a time. This will help you determine which one is causing the error.
In my case, I did just that, and when I imported the latter, the application was compiled. So I think the real problem was that I imported too much at once. But now everything works.
Another possible error question is its errors, clean gradle before assembly
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