public void set(String headerName, @Nullable String value) {
        String normalName = HeaderName.normalize(Objects.requireNonNull(headerName, "headerName"));
        setNormal(headerName, normalName, value);
    }
Replace any/all entries with this key, with this single entry.

If value is {@code null}, then not added, but any existing header of same name is removed.
zuul-core/src/main/java/com/netflix/zuul/message/Headers.java