code: public boolean getRequiredBoolean(String key) {
          Boolean value = configuration.getBoolean(key, null);
          if (value != null) {
              return value;
          } else {
              throw new IllegalStateException(String.format("required key [%s] not found", key));
          }
      }
docs: Return the boolean property value associated with the given key (never {@code null}).
  
  @return The boolean property
  @throws IllegalStateException if the key cannot be resolved