Use better way to check if logged in

client/src/components/Header.vue

@@ -41,7 +41,8 @@ async function signout(ev) {
 
         <div class="offcanvas-body px-2">
           <ul class="navbar-nav justify-content-end flex-grow-1 pe-3">
-            <li v-if="modelValue !== ''" class="nav-item mx-2 mt-2">
+            <!--<li v-if="modelValue !== ''" class="nav-item mx-2 mt-2">-->
+            <li v-if="modelValue.hasOwnProperty('username')" class="nav-item mx-2 mt-2">
               <button @click="signout" class="btn btn-outline-success">Sign out</button>
             </li>
             <li class="nav-item mf-3 mt-1">