code: public Class<?> getClass(String property) {
      return getProperty(property, className -> {
        try {
          return Class.forName(className);
        } catch (ClassNotFoundException e) {
          throw new ConfigurationException("unknown class: " + className, e);
        }
      });
    }
docs: Reads a class property.
  
  @param property The property name.
  @return The property value.
  @throws ConfigurationException if the property is not present