mongoose findById would not work with correct Id - node.js

Question

I was creating a database storing user information. Previously, the system worked well, after I performed npm update of mongoose, the system failed and I dont know why. The following is the error message I encountered.
CastError: Cast to ObjectId failed for value "xxxxxxxxxxxxxxx" at path "_id" for model "User"
Then, I write some simple testing code to test if the database is connected successfully. For example:
User.findOne({firstName: "David"}, function(err, user){console.log(user.lastName)});
The above worked perfectly.
I then found the corresponding Id from the database directly and create variable like:
var testId = "abcde"
and tried the following code:
User.findById(testId, function(err, user){console.log(user.firstName)});
Then it just output the error messages.
I have tried mongoose.Types.ObjectId.isValid('abcde') (abcde is just example) and it returned true. Therefore, I really have no ideas why it did not work...is it a mongoose bug?
Please help if you know the answer, thank you very much!

Answer 1

I just solved the problem.
As I mentioned, the findById function did not work after I updated mongoose. I was struggling on the code for few days and when I woke up this morning, I suddenly thought of upgrading my node.js.
That worked.
After upgrading node.js from v4.x.x to latest version, everything worked fine : )
This taught me a lesson that I should not upgrade a single module alone and care of compatibility issue.