Bug 38729 [Preferences] NPE PreferencePage isValid
getContainer may return null
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferencePage.java
* </p>
	 *
	 * @param parent the button bar
	 */
	protected void contributeButtons(Composite parent) {
	}
	/**
	 * Creates and returns the SWT control for the customized body 
	 * of this preference page under the given parent composite.
	 * <p>
	 * This framework method must be implemented by concrete subclasses. Any
	 * subclass returning a <code>Composite</code> object whose <code>Layout</code>
	 * has default margins (for example, a <code>GridLayout</code>) are expected to
	 * set the margins of this <code>Layout</code> to 0 pixels. 
	 * </p>
	 *
	 * @param parent the parent composite
	 * @return the new control
	 */
	protected abstract Control createContents(Composite parent);
	/**
	 * The <code>PreferencePage</code> implementation of this 
	 * <code>IDialogPage</code> method creates a description label
	 * and button bar for the page. It calls <code>createContents</code>
	 * to create the custom contents of the page.
	 * <p>
	 * If a subclass that overrides this method creates a <code>Composite</code>
	 * that has a layout with default margins (for example, a <code>GridLayout</code>)
	 * it is expected to set the margins of this <code>Layout</code> to 0 pixels.
	 */