Bug 38729 [Preferences] NPE PreferencePage isValid
getContainer may return null
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferencePage.java
control.setSize(uiSize);
			size = uiSize;
		}
	}
	/**
	 * The <code>PreferencePage</code> implementation of this <code>IDialogPage</code>
	 * method extends the <code>DialogPage</code> implementation to update
	 * the preference page container title. Subclasses may extend.
	 */
	public void setTitle(String title) {
		super.setTitle(title);
		if (getContainer() != null)
			getContainer().updateTitle();
	}
	/**
	 * Sets whether this page is valid.
	 * The enable state of the container buttons and the
	 * apply button is updated when a page's valid state 
	 * changes.
	 * <p>
	 *
	 * @param b the new valid state
	 */
	public void setValid(boolean b) {
		boolean oldValue = isValid;
		isValid = b;
		if (oldValue != isValid) {
			
			getContainer().updateButtons();