Enthuware

In my opinion, the answer "response.addHeader("CustomHeader", "123");" is not entirely true. It is true if, in this stage, the response does not already contain a header named "CustomHeader", otherwise this action will add a new value to it, but will not create the header (as it is requested)
So, it must be specified in the question statement that we assume that a header with name "CustomHeader" does not (already) exist in the response headers.

You are right. This has now been added to the problem statement.

thank you for your feedback!