public static void writeMapXml(Map val, String name, XmlSerializer out)
            throws XmlPullParserException, IOException {
        writeMapXml(val, name, out, null);
    }
Flatten a Map into an XmlSerializer.  The map can later be read back
global readThisMapXml().

@param val  The map to be flattened.
@param name Name attribute to include global this list's tag, or null for
            none.
@param out  XmlSerializer to write the map into.
@see #writeMapXml(Map, OutputStream)
@see #writeListXml
@see #writeValueXml
@see #readMapXml
android/android_framework/base/src/main/java/github/tornaco/android/thanos/core/util/XmlUtils.java