public void setHeaders(Multimap<String, String> headers) {
        this.headers = headers;
    }
@return the headers as a map; The map does not support {@code put} or {@code putAll}, nor do
its entries support {@link Entry#setValue setValue}, so you can't use this to add headers.
tika-pipes/tika-fetchers/tika-fetcher-http/src/main/java/org/apache/tika/pipes/fetcher/http/config/HttpHeaders.java