Allow an empty keySpec for Spacer

        mActionFlags = actionFlags;

        final String keySpec = style.getString(keyAttr, R.styleable.Keyboard_Key_keySpec);

        if (TextUtils.isEmpty(keySpec)) {

            throw new RuntimeException("Empty keySpec");

        // Note: {@link Spacer} has an empty keySpec.

        // TODO: Create a Key constructor that parses only key geometries and share it with Spacer.

        if (TextUtils.isEmpty(keySpec) && !(this instanceof Spacer)) {

            throw new RuntimeException("Empty keySpec found in " + getClass().getName());

        }

        mIconId = KeySpecParser.getIconId(keySpec);