Fica assim no listaconvidados.html?
<form action="delete/{id}" method="post">
<div class="form-group">
<label for="id">Id</label> <input type="text"
class="form-control" id="id" name="id"
placeholder="id" />
<button type="submit" class="btn btn-success">Deletar</button>
</div>
</form>
Ta aparecendo o seguinte erro:
Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.
Wed Apr 26 14:16:45 BST 2017
There was an unexpected error (type=Internal Server Error, status=500).
The entity must not be null!; nested exception is java.lang.IllegalArgumentException: The entity must not be null!