SubmitButton without caption throws depracated error on render on PHP 8.1

[martenb]

Version: 3.1.10
PHP: 8.1

Bug Description

Error

htmlspecialchars(): Passing null to parameter #1 ($string) of type string is deprecated

Generated code

echo htmlspecialchars($ʟ_input->getCaption()) /* line 2 */;

Steps To Reproduce

$form = new Form();
$form->addSubmit('send');

{form form}
	<button n:name="send"/>
{/form}

Expected Behavior

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Possible Solution

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