Bug 38729 [Preferences] NPE PreferencePage isValid
getContainer may return null
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferencePage.java
String title,
		String message) {
		Composite messageComposite = new Composite(composite, SWT.NONE);
		GridLayout messageLayout = new GridLayout();
		messageLayout.numColumns = 2;
		messageLayout.marginWidth = 0;
		messageLayout.marginHeight = 0;
		messageComposite.setLayout(messageLayout);
		messageComposite.setLayoutData(
			new GridData(GridData.HORIZONTAL_ALIGN_FILL));
		messageComposite.setFont(font);
		final Label noteLabel = new Label(messageComposite, SWT.BOLD);
		noteLabel.setText(title);
		noteLabel.setFont(JFaceResources.getBannerFont());
		noteLabel.setLayoutData(
			new GridData(GridData.VERTICAL_ALIGN_BEGINNING));
		final IPropertyChangeListener fontListener =
			new IPropertyChangeListener() {
			public void propertyChange(PropertyChangeEvent event) {
				if (JFaceResources.BANNER_FONT.equals(event.getProperty())) {
					noteLabel.setFont(
						JFaceResources.getFont(JFaceResources.BANNER_FONT));
				}
			}
		};
		JFaceResources.getFontRegistry().addListener(fontListener);
		noteLabel.addDisposeListener(new DisposeListener() {
			public void widgetDisposed(DisposeEvent event) {
				JFaceResources.getFontRegistry().removeListener(fontListener);
			}