Spring pre-fill form doesn't work

I created a form based on a form object.

I pre-filled the form object then display it, but some fields are displayed and some other no.

This is an exemple of a field that give problem:

JSP :

<tr>
        <td class="label"><a class="required"></a><spring:message code="service.userNumber" /></td>
        <td class="value">
                <form:select path="userNumber">
                    <form:option label="" value="" />
                    <form:options items="${serviceModelList}" itemLabel="description" itemValue="description" />
                </form:select>
                <form:errors path="userNumber" cssClass="errormsg" />
        </td>
</tr>

A part of my Form Object :

@NotEmpty
private String userNumber;

 public DeviceRequestForm(IDeviceRequest deviceRequest) {
    this.id = String.valueOf(deviceRequest.getId());
    this.site = deviceRequest.getSite();
    this.category = deviceRequest.getServiceCategory().getDescription();
    this.userNumber = deviceRequest.getServiceModelDescription(); //this is not null
    this.validator = deviceRequest.getValidator().getUsername();
    this.status = deviceRequest.getStatus();
    if (deviceRequest.getDeviceModel() != null) {
        this.deviceModel = deviceRequest.getDeviceModel().getModel();
    }
}

public String getUserNumber() {
    return userNumber;
}

public void setUserNumber(String userNumber) {
    this.userNumber = userNumber;
}

A part of my controller :

uiModel.addAttribute(WebConstants.DEVICE_REQUEST_FORM, new DeviceRequestForm(deviceRequest));
return ViewConstants.NEW_REQUEST_DEVICE_VIEW;