public O fromProtoEnum(E protoEnum) throws GeneralSecurityException {
    O objectEnum = fromProtoEnumMap.get(protoEnum);
    if (objectEnum == null) {
      throw new GeneralSecurityException("Unable to convert proto enum: " + protoEnum);
    }
    return objectEnum;
  }
Converts {@code protoEnum} to the equivalent object enum.
java_src/src/main/java/com/google/crypto/tink/internal/EnumTypeProtoConverter.java