presto-main/src/main/java/io/prestosql/server/HttpRequestSessionContext.java/HttpRequestSessionContext/parseClientTags
class HttpRequestSessionContext:    private Set<String> parseClientTags(HttpServletRequest servletRequest)
    {
        Splitter splitter = Splitter.on(',').trimResults().omitEmptyStrings();
        return ImmutableSet.copyOf(splitter.split(nullToEmpty(servletRequest.getHeader(PRESTO_CLIENT_TAGS))));
    }