Do not hard code placeholder aleksis banner in Vue code

aleksis/core/assets/components/BrandLogo.vue

 <template>
   <img
-    :src="
-      sitePreferences.themeLogo
-        ? sitePreferences.themeLogo.url
-        : '/static/img/aleksis-banner.svg'
-    "
+    :src="sitePreferences.themeLogo.url"
     :alt="sitePreferences.generalTitle + ' – Logo'"
     style="width: 100%"
   />

aleksis/core/schema/site_preferences.py

 import graphene
+from django.templatetags.static import static
 
 
 class ThemeLogoType(graphene.ObjectType):
@@ -21,7 +22,7 @@ class SitePreferencesType(graphene.ObjectType):
         return parent["general__title"]
 
     def resolve_theme_logo(parent, info, **kwargs):
-        return parent["theme__logo"]
+        return parent["theme__logo"] if parent["theme__logo"] else {"url": static("/img/aleksis-banner.svg")}
 
     def resolve_theme_primary(parent, info, **kwargs):
         return parent["theme__primary"]