private static InputStream createMapFileInputStream(final Uri mapUri) {
        if (mapUri == null) {
            return null;
        }
        return ContentStorage.get().openForRead(mapUri, true);
    }
Tries to open given uri as a mapfile.
If mapfile is invalid in any way (not available, not readable, wrong version, ...), then null is returned.
If mapfile is valid, then its attribution is read and returned (or a default attribution value in case attribution is null)
main/src/main/java/cgeo/geocaching/maps/mapsforge/MapsforgeMapProvider.java