@Override
  @SuppressWarnings("unchecked")
  public <T extends Serializable> T getCachedValue(String idempotentId) {
    if (!knownValues.containsKey(idempotentId)) {
      throw new IllegalArgumentException(
          idempotentId
              + " is not a known key, known keys: "
              + Joiner.on(", ").join(knownValues.keySet()));
    }
    return (T) knownValues.get(idempotentId);
  }
A {@link IdempotentImportExecutor} that stores known values in memory.
portability-spi-transfer/src/main/java/org/datatransferproject/spi/transfer/idempotentexecutor/RetryingInMemoryIdempotentImportExecutor.java