code: public Map<String, Object> getExtra() {
          if (extra == null) {
              // `extra` *should* never be null, but there are scenarios such as
              // when an application is run through ProGuard which may cause deserialization
              // code to be removed (and thus silently not run). In this case, our overridden
              // `readObject` may never be called and `extra` will remain null. :(
              extra = new HashMap<>();
              _logger.warn("`extra` field was null, deserialization must not have been called,"
                      + " please check your ProGuard (or other obfuscation) configuration.");
          }
  
          return extra;
      }
docs: CHECKSTYLE.OFF: JavadocMethod