I am not sure if this is the correct way, but it works. Change the form to:
<form th:action="@{/happyEat/shopping-lists/create}"
th:method="POST"
th:object="${__${objectForForm}__}">
and in the call hand over a String:
<div th:replace="~{fragment/form :: formWithContent(
~{fragment/shopping-list/input :: create},
'shoppingListCreateRequest)'}">
</div>