code: private void put(String section, String key, String value, boolean append) {
          // ignore lines without =
          if (key == null) {
              return;
          }
          if (section == null) {
              put(key, value, append);
              return;
          }
          put(key.isEmpty()
                          ? section
                          : section + '.' + key,
                  value, append);
      }
docs: Adds accumulated value to key and current section.