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>