private boolean setIfAbsentNormal(String originalName, String normalName, String value) {
        int i = findNormal(normalName);
        if (i != ABSENT) {
            return false;
        }
        addNormal(originalName, normalName, value);
        return true;
    }
Adds the name and value to the headers, except if the name is already present.  Unlike
{@link #set(HeaderName, String)}, this method does not accept a {@code null} value.

@return if the value was successfully added.
zuul-core/src/main/java/com/netflix/zuul/message/Headers.java