code: private static @Nullable SecretKey loadSymmetricKey(Context context, KeyPair wrapperKey) throws NoSuchPaddingException,
  	                                                                                                NoSuchAlgorithmException,
  	                                                                                                InvalidKeyException {
  		String encryptedSymmetricKey = getKeyPrefs(context).getString(PREFS_KEY_SYMMETRIC_KEY, null);
  		if (StringUtils.isNullOrEmpty(encryptedSymmetricKey)) {
  			return null;
  		}
  
  		return unwrapSymmetricKey(wrapperKey, encryptedSymmetricKey);
  	}
docs: Attempts to load an existing symmetric key or return <code>null</code> if failed.
  Multistep process:
  1. Load and encrypted symmetric key data from the shared preferences.
  2. Unwraps the key using <code>wrapperKey</code>