Grails SpringSecurityService: Cannot get property 'principal' on null object

I'm writing an update or change user data form in Grails. This is a part of my form, where user can change his old login:

<g:form class="form-signin" controller="VisitorSpace">
            <label for="login" class="sr-only">Логин</label>
            <g:textField id="login" class="form-control" name="login" placeholder="Логин" value="${springSecurityService.principal.username}" required="" autofocus=""/>
...
</g:form>

Old user data must be shown before update. I use for it: ${springSecurityService.principal.username} But when I run this page I get such error:

Error 500: Internal Server Error
URI:/restorator/visitorSpace/editPrivateDataClass:java.lang.NullPointerExceptionMessage:Cannot get property 'principal' on null object

How to fix it?