@Override
    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
        // Serialize as primitive
        return string.append(function.toPrimitive().toString(new ExpressionToStringContext(context, path, this)));
    }
Returns the tensor function wrapped by this
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/TensorFunctionNode.java