Bug 38729 [Preferences] NPE PreferencePage isValid
getContainer may return null
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferencePage.java
data.heightHint = heightHint;
			data.widthHint =
				Math.max(
					widthHint,
					applyButton.computeSize(SWT.DEFAULT, SWT.DEFAULT, true).x);
			applyButton.setLayoutData(data);
			applyButton.addSelectionListener(new SelectionAdapter() {
				public void widgetSelected(SelectionEvent e) {
					performApply();
				}
			});
			applyButton.setEnabled(isValid());
		} else {
			/* Check if there are any other buttons on the button bar.
			 * If not, throw away the button bar composite.  Otherwise
			 * there is an unusually large button bar.
			 */
			if (buttonBar.getChildren().length < 1)
				buttonBar.dispose();
		}
	}
	/**
	 * Creates and returns an SWT label under the given composite.
	 *
	 * @param parent the parent composite
	 * @return the new label
	 */
	protected Label createDescriptionLabel(Composite parent) {
		Label result = null;
		String description = getDescription();