Failing test (same for TreeTablePosition):

    @Test
    public void testNullTable() {
        new TablePosition<>(null, 2, new TableColumn<>());
    }
    
As null handling is not spec'ed in the constructor's doc, options to fix would be

- change the doc to explicitly disallow null
- fix the implementation to not throw

My take is clearly the latter (in no particular order):

- a position might be used unrelated to a specific table: used to mark f.i. a particular cell in any table
- users are warned to expect a null (f.i. in doc of constructor and getColumn), so formally supporting it wouldn't make a difference to client code
- the NPE (for TableView) is introduced in JDK-8093105, looks like it happend accidentally when supporting access to the underlying row object

blowing code:

    List<S> items = tableView.getItems();

fix to

    List<S> items = tableView != null ? tableView.getItems() : null;