public void writeStringMap(DataOutput out, Map<String, String> stringMap) throws IOException {
        strategy.writeStringMap(out, stringMap);
    }
Writes a Map of String key and value pairs. This method handles the
case when the Map is {@code null}.

@param out       the output stream.
@param stringMap the Map of String key/value pairs.
@throws java.io.IOException if an error occurs.
xmppserver/src/main/java/org/jivesoftware/util/cache/ExternalizableUtil.java