public final void mustAdd(E newElement) {
        if (!add(newElement)) {
            throw new RuntimeException("Unable to add " + newElement);
        }
    }
Add a new element to the collection.

@param newElement    The new element.

@return              True if the element was added to the collection;
                     false if it was not, because there was an existing equal element.
clients/src/main/java/org/apache/kafka/common/utils/ImplicitLinkedHashCollection.java