How to check if key exists on mongoose document?

I have a User Model and recently added some key to it. This means that existing users will not have this key initially and new users do. Now I have a route where I want to check if the particular key exists on the user object so that I can add it if it returns false.

This is my route currently:

router.post("/new-application", verifyUser, (req, res) => {
  const { application } = req.body;
  User.findById(req.userId)
    .then((user) => {
      if (user.hasOwnProperty("applications")) {
        console.log("has applications");
      } else {
        console.log("has not applications");
        user["applications"] = initialApplications;
      }
      user.save().then((updatedUser) => {
        // console.log(updatedUser);
      });
    })
    .catch((err) => {
      console.log("err fetching user: ", err);
      res.end();
    });
});

The problem is that if (user.hasOwnProperty("applications")) always returns false even after I added it to the user. I also tried if("applications" in user). That also does not work.

So how can I check if a key or field exists on a Mongoose object.