public static void setPersistableUri(@NonNull final PersistableUri persistedUri, @Nullable final String uri) {
        putString(persistedUri.getPrefKeyId(), uri);
        handleLegacyValuesOnSet(persistedUri.getPrefKeyId());
    }
sets Uri for persistable uris. Can be set to null
should be called by PersistableUri class only
main/src/main/java/cgeo/geocaching/settings/Settings.java