public void setIfValid(String headerName, @Nullable String value) {
        Objects.requireNonNull(headerName, "headerName");
        if (isValid(headerName) && isValid(value)) {
            String normalName = HeaderName.normalize(headerName);
            setNormal(headerName, normalName, value);
        }
    }
Replace any/all entries with this key, with this single entry if the key and entry are valid.

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