public void writeSerializableMap(DataOutput out, Map<? extends Serializable, ? extends Serializable> map) throws IOException {
        writeObject(out, map);
    }
Writes a Map of Serializable key and value pairs. This method handles the
case when the Map is <tt>null</tt>.

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