Fixed issue when user doesnt exist

Fixed button hover color

app/assets/stylesheets/pages/issuable.scss

@@ -242,7 +242,7 @@
     }
   }
 
-  a {
+  a:not(.btn) {
     &:hover {
       color: $md-link-color;
       text-decoration: none;
@@ -291,14 +291,5 @@
 
   a {
     color: #8c8c8c;
-
-    &:hover {
-      color: $gl-text-color;
-      text-decoration: none;
-    }
-
-    &:focus {
-      text-decoration: none;
-    }
   }
 }

app/views/shared/issuable/_sidebar.html.haml

@@ -21,7 +21,7 @@
 
     = form_for [@project.namespace.becomes(Namespace), @project, issuable], remote: true, html: {class: 'issuable-context-form inline-update js-issuable-update'} do |f|
       .block.assignee
-        .sidebar-collapsed-icon.sidebar-collapsed-user{data: {toggle: "tooltip", placement: "left", container: "body"}, title: issuable.assignee.to_reference}
+        .sidebar-collapsed-icon.sidebar-collapsed-user{data: {toggle: "tooltip", placement: "left", container: "body"}, title: (issuable.assignee.to_reference if issuable.assignee)}
           - if issuable.assignee
             = link_to_member_avatar(issuable.assignee, size: 24)
           - else