public ListMap<String, String> getHeaders(boolean create) {
        if (headers == null && create)
            headers = new ListMap<>();
        return headers;
    }
Returns the set of "envelope" headers to be returned with this result.
This returns the live map in modifiable form - modify this to change the
headers. Or null if none, and it should not be created.
<p>
Used for HTTP headers when the return protocol is HTTP, e.g
<pre>result.getHeaders(true).put("Cache-Control","max-age=120")</pre>

@param create if true, create the header ListMap if it does not exist
@return returns the ListMap of current headers, or null if no headers are set and <pre>create</pre> is false
container-search/src/main/java/com/yahoo/search/Result.java