Bug 49182 What should canceling setRawClasspath do ?
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/VariableBlock.java
public void customButtonPressed(ListDialogField field, int index) {
			switch (index) {
			case 0: 
				editEntries(null);
				break;
			case 1: 
				List selected= field.getSelectedElements();			
				editEntries((CPVariableElement)selected.get(0));
				break;
			}
		}
		
		public void selectionChanged(ListDialogField field) {
			doSelectionChanged(field);
		}
		
		public void doubleClicked(ListDialogField field) {
			if (fInPreferencePage) {
				List selected= field.getSelectedElements();
				if (canEdit(selected, containsReserved(selected))) {
					editEntries((CPVariableElement) selected.get(0));
				}
			}
		}