getMacAddress() liefert null zurück

Codebeispiel:
/* This will generate a single Type 4 pseudo random UUID */
public UUID genRandomUID() {

return UUID.randomUUID();
}

/** a more sophisticated variant then the above, putting the one time UUID into shared *Preference
*Thanks to Reto Meier for this convienience method! **/

private static String uniqueID = null;
private static final String PREF_UNIQUE_ID = "PREF_UNIQUE_ID";

public synchronized static String id(Context context) {
if (uniqueID == null) {
SharedPreferences sharedPrefs = context.getSharedPreferences(
PREF_UNIQUE_ID, Context.MODE_PRIVATE);
uniqueID = sharedPrefs.getString(PREF_UNIQUE_ID, null);
if (uniqueID == null) {
uniqueID = UUID.randomUUID().toString();
Editor editor = sharedPrefs.edit();
editor.putString(PREF_UNIQUE_ID, uniqueID);
editor.commit();
}
}
return uniqueID;
}