Is it possible to compose elements conditionally?

[griffrawk]

I'd like to be able to compose elements conditionally to avoid too much code duplication.

My code draws a rectangle, and overlays it with some text. I want to be able to use a flag to conditionally control the addition of the Text element based upon e.g. the block size being too small to fit visible text within it. Otherwise I have to move the condition outside and make a choice between returning Rectangle + Text, or just Rectangle.

EmptyElement::at((x, y))
    + Rectangle::new(
    [(0, 0), (block_side, block_side)],
    ShapeStyle::from(&bg_colour).filled(),
)
// if some_flag {
    + Text::new(
    format!("{}", node.f_est_cost),
    (10, 10),
    ("sans-serif", 30).into_font().color(&fg_colour)
)
// }

I've tried something like this, using .add to no avail:

let mut block = EmptyElement::at((x, y))
    + Rectangle::new(
    [(0, 0), (block_side, block_side)],
    ShapeStyle::from(&bg_colour).filled(),
);
if some_flag {
    block.add(Text::new(
    format!("{}", node.f_est_cost),
    (10, 10),
    ("sans-serif", 30).into_font().color(&fg_colour)
    ))
};

block