Bug 38729 [Preferences] NPE PreferencePage isValid
getContainer may return null
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferencePage.java
return null;
	}
	/**	
	 * The preference page implementation of an <code>IPreferencePage</code>
	 * method returns whether this preference page is valid. Preference
	 * pages are considered valid by default; call <code>setValid(false)</code>
	 * to make a page invalid.
	 */
	public boolean isValid() {
		return isValid;
	}
	/**
	 * Suppresses creation of the standard Default and Apply buttons
	 * for this page.
	 * <p>
	 * Subclasses wishing a preference page wihthout these buttons
	 * should call this framework method before the page's control
	 * has been created.
	 * </p>
	 */
	protected void noDefaultAndApplyButton() {
		createDefaultAndApplyButton = false;
	}
	/**
	 * The <code>PreferencePage</code> implementation of this 
	 * <code>IPreferencePage</code> method returns <code>true</code>
	 * if the page is valid.
	 */
	public boolean okToLeave() {
		return isValid();