code: public static String getString(
      final Properties properties,
      final String key)
      throws JPropertyNonexistent
    {
      Objects.requireNonNull(properties, "Properties");
      Objects.requireNonNull(key, "Key");
  
      final String value = properties.getProperty(key);
      if (value == null) {
        throw notFound(key);
      }
      return value;
    }
docs: <p> Returns the string value associated with {@code key} in the
  properties referenced by {@code props} </p>
  
  @param properties The loaded properties.
  @param key        The requested key.
  
  @return The value associated with the given key
  
  @throws JPropertyNonexistent If the given key is not present in the given
  properties.