lookup-protolib/src/main/java/com/streamsets/pipeline/stage/processor/kv/OptionalLoadingCache.java
private Optional<Value> valueOrDefault(Key key, Optional<Value> value) {
    // If value is present simply return it
    if(value.isPresent()) {
      return value;
    }

    if(!cacheMissingValues) {
      delegate.invalidate(key);
    }

    return defaultValue;
  }
private Optional<Value> valueOrDefault(Key key, Optional<Value> value) {
    // If value is present simply return it
    if(value.isPresent()) {
      return value;
    }

    if(!cacheMissingValues) {
      delegate.invalidate(key);
    }

    return defaultValue;
  }
Internal method to ensure that we return and not cache the default value if needed