Consider code like:
```
$ cat /tmp/T.java
import java.lang.ref.*;
public class T {
    public static void main(String[] args) {
        new WeakReference<>(null) {
            private Object hardRef = null;
        };
    }
}
```
and compile it using current JDK 25 or current JDK 26:
```
$ ./jdk-25/bin/javac -fullversion
javac full version "25-ea+30-3419"
$ ./jdk-25/bin/javac /tmp/T.java
/tmp/T.java:4: error: modifier sealed not allowed here
        new WeakReference<>(null) {
                                  ^
1 error
$ ./jdk-26/bin/javac -fullversion
javac full version "26-ea+5-453"
$ ./jdk-26/bin/javac /tmp/T.java
/tmp/T.java:4: error: modifier sealed not allowed here
        new WeakReference<>(null) {
                                  ^
1 error
```

This is obviously completely incorrect.

Reported here:
https://github.com/apache/netbeans/pull/8572#issuecomment-3046371322