@Override
    protected final boolean shouldConvert(Expression expression) {
        if (transformClass.isInstance(expression)) {
            if (transformed) {
                duplicate = true;
                return true;
            }
            transformed = true;
            return false;
        }
        if ( ! requiresTransform(expression)) return false;
        if (transformed) return false;
        return true;
    }
Inserts a "newTransform()" before expressions that "requiresTransform()"

@author Simon Thoresen Hult
indexinglanguage/src/main/java/com/yahoo/vespa/indexinglanguage/ValueTransformProvider.java