Bug 55399 exception on Code Style preference page
Nightly build 0319 - start a new eclipse install - show the Java > Code Style preference page - will get the attached exception
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/preferences/NameConventionConfigurationBlock.java
private boolean canEdit(ListDialogField field) {
			return field.getSelectedElements().size() == 1;
		}
		public void customButtonPressed(ListDialogField field, int index) {
			doEditButtonPressed();
		}
		public void selectionChanged(ListDialogField field) {
			field.enableButton(0, canEdit(field));
		}
			
		public void doubleClicked(ListDialogField field) {
			if (canEdit(field)) {
				doEditButtonPressed();