public Key parseKeyWithLegacyFallback(
      ProtoKeySerialization protoKeySerialization, @Nullable SecretKeyAccess access)
      throws GeneralSecurityException {
    if (!hasParserForKey(protoKeySerialization)) {
      return new LegacyProtoKey(protoKeySerialization, access);
    }
    return parseKey(protoKeySerialization, access);
  }
Returns a Key object from a protoKeySerialization, even if no parser has been registered.

<p>Falling back is useful because we want users to be able to call {@code #getAt} even for key
types for which we did not yet register a parser; in this case we simply fall back to return a
LegacyProtoKey.

@throws GeneralSecurityException if a parser is registered but parsing fails or required
    SecretKeyAccess is missing
java_src/src/main/java/com/google/crypto/tink/internal/MutableSerializationRegistry.java