bad request when sending number to Spring controller

I have a form that sends some data to a controller, when I send only text data it works fine, but when I send a given type number (and that in the controller I expect to receive a Double parameter) gives bad request error. If any field is sent empty, I deal with jquery to identify the empty fields in a service (if the field is not filled the jquery fills with 'null' and then my service understands that it has not been filled).

Form

<form action="/pecas/teste" id="pesquisa">
                Descrição: 
                <input type="text" name="descricao" id="desc">
                Categoria:
                <input type="text" name="categoria" id="cat">
                Tamanho:
                <input type="text" name="categoria" id="tam">
                Cor:
                <input type="text" name="cor" id="cor">
                Preço:
                <input type="number" name="preco" id="preco">

                <input type="submit">
            </form>

Jquery

$("#pesquisa").submit(function(){
            if($("#desc").val() == '')
                $("#desc").val('null');

            if($("#cat").val() == '')
                $("#cat").val('null');

            if($("#tam").val() == '')
                $("#tam").val('null');

            if($("#cor").val() == '')
                $("#cor").val('null');

            //como não sei o que está dando errado
            //não tô fazendo o tratamento para preco

        });

Controller

@RequestMapping(path="/teste")
public ModelAndView mostrarPecas(@RequestParam String descricao, @RequestParam String categoria, @RequestParam String cor,
        @RequestParam String tamanho, @RequestParam Double preco) {

    ModelAndView mv = new ModelAndView("verpecas");

    List<Peca> pecas = service.getPecas(descricao, categoria, tamanho, cor, preco);

    mv.addObject("pecas", pecas);

    return mv;
}