Bug 130854 [CellEditors] JFace TableViewer ignoring ICellEditor validator state
Using a validator on a TextCellEditor and entering invalid text into a cell results in ICellModifier.modify() being called with a null value, rather than an error being reported and the value being discarded. TableEditorImpl.saveEditorValue() *does actually check for editor validity*, but in the case of invalid values does nothing but no-op with comment "///Do what ???" and then calls cellEditor.getValue() which, for TextCellEditor's anyway, always returns null if its validator has invalidated the current value.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ColumnViewerEditor.java
}
				setLayoutData(cellEditor.getLayoutData());
				setEditor(control, (Item) cell.getItem(), cell.getColumnIndex());
				cellEditor.setFocus();
				if (cellEditor.dependsOnExternalFocusListener()) {
					if (focusListener == null) {
						focusListener = new FocusAdapter() {
							public void focusLost(FocusEvent e) {
								applyEditorValue();
							}
						};
					}
					control.addFocusListener(focusListener);
				}
				mouseListener = new MouseAdapter() {
					public void mouseDown(MouseEvent e) {
						
						
						if (shouldFireDoubleClick(activationTime, e.time, activationEvent) && e.button == 1) {
							control.removeMouseListener(mouseListener);
							cancelEditing();
							handleDoubleClickEvent();
						} else if (mouseListener != null) {
							control.removeMouseListener(mouseListener);
						}
					}
				};
				if (activationTime != 0
						&& (feature & KEEP_EDITOR_ON_DOUBLE_CLICK) == 0) {
					control.addMouseListener(mouseListener);