Bug 38729 [Preferences] NPE PreferencePage isValid
getContainer may return null
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferencePage.java
extends DialogPage
	implements IPreferencePage {
	/**
	 * Preference store, or <code>null</code>.
	 */
	private IPreferenceStore preferenceStore;
	/**
	 * Valid state for this page; <code>true</code> by default.
	 *
	 * @see #isValid
	 */
	private boolean isValid = true;
	/**
	 * Body of page.
	 */
	private Control body;