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
}
	}
	private void saveEditorValue(CellEditor cellEditor) {
		ViewerColumn part = viewer.getViewerColumn(cell.getColumnIndex());
		if (part != null && part.getEditingSupport() != null) {
			part.getEditingSupport().saveCellEditorValue(cellEditor, cell);
		}
	}
	/**
	 * Return whether there is an active cell editor.
	 *
	 * @return <code>true</code> if there is an active cell editor; otherwise
	 *         <code>false</code> is returned.
	 */
	boolean isCellEditorActive() {
		return cellEditor != null;
	}
	void handleDoubleClickEvent() {
		viewer.fireDoubleClick(new DoubleClickEvent(viewer, viewer
				.getSelection()));
		viewer.fireOpen(new OpenEvent(viewer, viewer.getSelection()));
	}
	/**
	 * Adds the given listener, it is to be notified when the cell editor is
	 * activated or deactivated.
	 *
	 * @param listener
	 *            the listener to add
	 */
	public void addEditorActivationListener(