Set expireTimer to null to unset

// FREEBIE

js/models/conversations.js

@@ -199,6 +199,7 @@
     },
 
     updateExpirationTimer: function(expireTimer, source, received_at) {
+        if (!expireTimer) { expireTimer = null; }
         source = source || textsecure.storage.user.getNumber();
         var timestamp = received_at || Date.now();
         this.save({ expireTimer: expireTimer });

js/models/messages.js

@@ -424,7 +424,7 @@
                                       message.get('received_at'));
                                 }
                             } else if (conversation.get('expireTimer')) {
-                                conversation.updateExpirationTimer(0, source,
+                                conversation.updateExpirationTimer(null, source,
                                     message.get('received_at'));
                             }
                         }

js/views/conversation_view.js

@@ -32,8 +32,10 @@
         },
         setTimer: function(e) {
             var seconds = this.$(e.target).data().seconds;
-            if (seconds >= 0) {
+            if (seconds > 0) {
                 this.model.updateExpirationTimer(seconds);
+            } else {
+                this.model.updateExpirationTimer(null);
             }
         },
         render: function() {