show expiry only if available

src/components/mute_card/mute_card.js

@@ -13,6 +13,9 @@ const MuteCard = {
     muted () {
       return this.relationship.muting
     },
+    muteExpiryAvailable () {
+      return this.user.mute_expires_at !== undefined
+    },
     muteExpiry () {
       return this.user.mute_expires_at == null
         ? this.$t('user_card.mute_expires_forever')

src/components/mute_card/mute_card.vue

@@ -1,7 +1,7 @@
 <template>
   <basic-user-card :user="user">
     <div class="mute-card-content-container">
-      <span v-if="muted" class="alert neutral">
+      <span v-if="muted && muteExpiryAvailable" class="alert neutral">
         {{ muteExpiry }}
       </span>
       {{ ' ' }}