code: protected final String getValue(final String propertyName, String defaultValue) {
          String value = getValue(propertyName);
          if (value == null) {
              if (defaultValue == null) {
                  LOGGER.warn(
                          "Property '{}' is not specified in "
                          + getClass().getName()
                          + ", and no default is specified.", propertyName);
              }
              value = defaultValue;
          }
          return value;
      }
docs: Returns the String value of the given property name, or the given default
  if the given property name does not exist.
  
  @param propertyName The name of the property to fetch a value for.
  @param defaultValue The default value to return if the property name does
  not exist.
  @return A string containing either the value of the property, or the
  default value.