Erro: Neither BindingResult nor plain target object for bean name 'tarefa' available as request attribute
Solucionado
Erro: Neither BindingResult nor plain target object for bean name 'tarefa' available as request attribute
Corrigi o problema...
Adicionei:
No gravar():
@ModelAttribute("tarefa") No form():
Tarefa tarefa = new Tarefa();
modelAndView.addObject("tarefa", tarefa);