What does this operator do in PHP? [duplicate]

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• Reference - What does this symbol mean in PHP? 7 answers

I'm currently trying to resolve a bug in another programmers code (who I can't contact). His code is as follows;

$prooms = mysqli_query($con, "select * from property_room where property_id='".(int)$property_id ."'") or die(mysqli_error($con));
    while($r = mysqli_fetch_array( $prooms )) {
        $rooms[]=array(
                        "room_name" => $r['property_room_name'],
                        "room_description" => $r['property_room_description'] ,
                        "room_length" => $r['property_room_length']?$r['property_room_dimension_unit']:NULL ,
                        "room_width" => $r['property_room_width']?$r['property_room_dimension_unit']:NULL ,
                        "room_dimension_unit" => $r['property_room_dimension_unit']?$r['property_room_dimension_unit']:NULL ,
                        "room_photo_urls" =>$r['property_room_images_url'] 
                    );
    }

For the line;

"room_length" => $r['property_room_length']?$r['property_room_dimension_unit']:NULL ,

Does this mean if $r['property_room_length'] is empty the string is set to NULL?

What I'm trying to achieve is that if $r['property_room_length'] is set to '0.00' I want the string to be set to NULL.