code: public double getDouble(String property) {
      return getProperty(property, value -> {
        try {
          return Double.valueOf(value);
        } catch (NumberFormatException e) {
          throw new ConfigurationException("malformed property value: " + property + " must be a double");
        }
      });
    }
docs: Reads a double property.
  
  @param property The property name.
  @return The property value.
  @throws ConfigurationException if the property is not present