code: public String getValue(String propertyName) {
          Property property = super.get(propertyName);
          if (property == null) {
              return null;
          }
          return property.getValue();
      }
docs: Retrieves the value of a property.
  @param propertyName Name of the property (or key) in the configuration.
  
  @return the value of the specified property, or null if not found.