At least with current Valhalla prototype this happens:

$ cat Point.java
inline class Point {
  int x;
  int y;
  Point() { x = 0; y = 0; }
}

$ javac Point.java
$ java -jar ~/projects/jol/jol-cli/target/jol-cli.jar internals Point -cp .
...

Instantiated the sample instance via default constructor.

java.lang.IllegalArgumentException: cannot reference an inline value of type: Point
at java.base/java.lang.ref.Reference.<init>(Reference.java:401)
at java.base/java.lang.ref.Reference.<init>(Reference.java:395)
at java.base/java.lang.ref.WeakReference.<init>(WeakReference.java:62)
at org.openjdk.jol.info.ClassData.<init>(ClassData.java:139)
at org.openjdk.jol.info.ClassData.parse(ClassData.java:97)
at org.openjdk.jol.info.ClassData.parseInstance(ClassData.java:53)
at org.openjdk.jol.info.ClassLayout.parseInstance(ClassLayout.java:100)
at org.openjdk.jol.info.ClassLayout.parseInstance(ClassLayout.java:83)
at org.openjdk.jol.operations.ObjectInternals.runWith(ObjectInternals.java:51)
at org.openjdk.jol.operations.ClasspathedOperation.run(ClasspathedOperation.java:76)
at org.openjdk.jol.Main.main(Main.java:60)