getUUID: Return undefined if uuid is falsey

ts/models/conversations.ts

@@ -3497,7 +3497,7 @@ export class ConversationModel extends window.Backbone
   getUuid(): UUID | undefined {
     try {
       const value = this.get('uuid');
-      return value && new UUID(value);
+      return value ? new UUID(value) : undefined;
     } catch (err) {
       log.warn(
         `getUuid(): failed to obtain conversation(${this.id}) uuid due to`,

ts/textsecure/storage/User.ts

@@ -71,7 +71,7 @@ export class User {
       `Unsupported uuid kind: ${uuidKind}`
     );
     const uuid = this.storage.get('uuid_id');
-    if (uuid === undefined) return undefined;
+    if (!uuid) return undefined;
     return new UUID(Helpers.unencodeNumber(uuid.toLowerCase())[0]);
   }