** (Middleware) - Automatically sets headers in each request, so you don't have to!** ** Only non-existing header values are set, leaving any existing values untouched. This means you can use sticky ** headers to set default values and manually override them for individual requests.class StickyHeadersMiddleware : ButterMiddleware {** The header values set in every request HttpRequestHeaders headers := HttpRequestHeaders() @NoDoc @Deprecated { msg="Use 'headers' instead"} HttpRequestHeaders stickyHeaders(){ headers } @NoDocoverride ButterResponse sendRequest(Butter butter, ButterRequest req){ headers.val.each |val, key| {if(!req.headers.containsKey(key)) req.headers[key] = val}return butter.sendRequest(req)}** Getter for sticky header values. @Operator Str? get(Str key){ headers[key]}** Setter for sticky header values.** Setting a 'null' value removes the value from the map. @Operator Void set(Str key, Str? val){ headers[key] = val}}