Hi @lhazlewood, I would like to create a PR (as part of hacktoberfest) to resolve this bug. I propose to implement DefaultCollectionMutator.replace(E e) which internally call remove(E e) then doAdd(E e), something like:

public M replace(E e) {
    this.collection.remove(e);
    doAdd(e);

    // triger changed() callback accordingly
    if (...) changed();

    return self();
}

I have decided that DefaultCollectionMutator would be a good place to implement this since:

• DefaultJwtParserBuilder.sig() returns new DefaultNestedCollection
• DefaultNestedCollection extends DefaultCollectionMutator
• DefaultCollectionMutator contains add(E e) and remove(E e) called in your sample code.

I am also running my idea through as I am not confident if it might bring about any security concerns.

I would appreciate any comments on (the feasibility of) my proposed solution, Thank you.

@lhy-hoyin Sorry for the delay, I had a minor family emergency and haven't been able to look at this, but I will be able to in about a week. @bdemers would you be able to look? Thanks for the Hacktobertest work!

@lhy-hoyin Sounds good, please send a pull request!

My suggestion would be to think about the unit tests too.
The proposed functionality is very similar to the current add method, though likely may need to handle a null item differently.

Let us know when you have a PR ready and we will take a look!