private void setNormal(String originalName, String normalName, @Nullable String value) {
        int i = findNormal(normalName);
        if (i == ABSENT) {
            if (value != null) {
                addNormal(originalName, normalName, value);
            }
            return;
        }
        if (value != null) {
            value(i, value);
            originalName(i, originalName);
            i++;
        }
        clearMatchingStartingAt(i, normalName, /* removed= */ null);
    }
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