This Bugzilla instance is a read-only archive of historic NetBeans bug reports. To report a bug in NetBeans please follow the project's instructions for reporting issues.
A method that returns com.google.common.collect.ImmutableCollection (or its subclasses) should not the "return of Collection field" warning since there is no thread-safety risk.
Perhaps a better approach would be to convince the Guava project to mark up their classes using @Immutable (JSR305) and scan for that instead? Let me know what you think.
There is also @ThreadSafe (Immutable implies thead-safe but I think you'd have to scan for both annotations separately).