The example has a custom TableCell that uses the row's item to configure its own visuals. To reproduce the NPE, compile and run

- note that the cells' content is not fully visible (no wonder, we set the column's pref too small ;)
- double click the column's resize region to adjust its width
- expected: column width extended to fit the cell content
- actual: NPE thrown (and column width unchanged)

Technically, the reason is that the row is actually null (due to the cell context not completely setup for measuring its size requirement JDK-8251480).

This behavior is unexpected: client code shouldn't be required to bother with implementation details for certain use-cases but rely on a fully configured cell context if !cell.empty.

The example:

    public class TableColumnAutoSizingNPE extends Application {
    
        private Parent createContent() {
            TableView<String> table = new TableView<>(FXCollections.observableArrayList
                    ("short name", "and now really really longish name that exceeds all"));
            TableColumn<String, String> name = new TableColumn<>("Name");
            // just for control (without, it will throw initially)
            name.setPrefWidth(100);
            name.setCellValueFactory(cc -> new SimpleStringProperty(cc.getValue()));
            name.setCellFactory(cc -> new TableCell<String, String>() {
    
                @Override
                protected void updateItem(String item, boolean empty) {
                    super.updateItem(item, empty);
                    if (empty) {
                        setText("");
                    } else {
                        // access item of tableRow:
                        // NPE on autosizing because row is null
                        setText(item + getTableRow().getItem());
                    }
                }
                
            });
            table.getColumns().addAll(name);
            BorderPane content = new BorderPane(table);
            return content;
        }
    
        @Override
        public void start(Stage stage) throws Exception {
            stage.setScene(new Scene(createContent(), 400, 200));
            //stage.setTitle(FXUtils.version());
            stage.show();
        }
    
        public static void main(String[] args) {
            launch(args);
        }
    
    }