Previously, when a project contained multiple `@ServletComponentScan`
annotated classes in classpath, and at least one annotation don't
explicitly specify `basePackages` and `basePackageClass` attribute,
the application could fail to start with an
UnsupportedOperationException. The failure occurred due to the
creating of an unmodifiable set when no base packages are configured
and a subsequent attempt to add base packages to that sit.
This commit fixes the issue by removing the use of an unmodifiable set
when `@ServletComponentScan` with no base packages in processed before
any other `@ServletComponentScan` annotations.
See gh-12715
7bec780281