MapValueRetrievalExample.java

public String ofNullableExample(Map<String, String> map) {
  return Optional.ofNullable(map.get(key))
    .orElseThrow(() -> new ItemNotFoundException(key));
}

public String nullCheckingExample(Map<String, String> map) {
  String valueAtKey = map.get(key);
  if (valueAtKey == null) {
    throw new ItemNotFoundException(key);
  }
  return valueAtKey;
}