code: public int getRequiredInt(String key) {
          Optional<Integer> value = getInteger(key);
          if (value.isPresent()) {
              return value.get();
          }
          throw new IllegalStateException(String.format("required key [%s] not found", key));
      }
docs: Return the int property value associated with the given key (never {@code null}).
  
  @return The int property
  @throws IllegalStateException if the key cannot be