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