Renders '$name=""' if $value is an empty string.
\Drupal\Core\Template\AttributeValueBase::render()
const RENDER_EMPTY_ATTRIBUTE = TRUE;
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https://api.drupal.org/api/drupal/core!lib!Drupal!Core!Template!AttributeValueBase.php/constant/AttributeValueBase::RENDER_EMPTY_ATTRIBUTE/8.1.x