Make sure we get valid package name or fail.

        final IMountService mountService = IMountService.Stub.asInterface(

                ServiceManager.getService("mount"));

        try {

            final String packageName = ActivityThread.currentOpPackageName();

            String packageName = ActivityThread.currentOpPackageName();

            if (packageName == null) {

                // Package name can be null if the activity thread is running but the app

                // hasn't bound yet. In this case we fall back to the first package in the

                // current UID. This works for runtime permissions as permission state is

                // per UID and permission realted app ops are updated for all UID packages.

                String[] packageNames = ActivityThread.getPackageManager().getPackagesForUid(

                        android.os.Process.myUid());

                if (packageNames == null || packageNames.length <= 0) {

                    return new StorageVolume[0];

                }

                packageName = packageNames[0];

            }

            final int uid = ActivityThread.getPackageManager().getPackageUid(packageName, userId);

            if (uid <= 0) {

                return new StorageVolume[0];

            }

            return mountService.getVolumeList(uid, packageName);

        } catch (RemoteException e) {

            throw e.rethrowAsRuntimeException();