code: protected HandledOptionalPath handleOptionalPathMapping(String paramPath) {
          // #for_now no considering type difference: index(String, OptionalThing<Integer>) but 'sea/land'
          // so cannot mapping to dockside(String hangar) if the index() exists now
          if (hasOptionalPathParameter()) { // e.g. any parameters are optional type
              if (indexMethod) { // e.g. index(String first, OptionalThing<String> second) with 'sea' or 'sea/land'
                  final int paramCount = Srl.count(Srl.trim(paramPath, "/"), "/") + 1; // e.g. sea/land => 2
                  return determineOptionalPath(paramPath, paramCount, /*namedMethod*/false);
              } else { // e.g. sea(String first, OptionalThing<String> second) with 'sea/dockside' or 'sea/dockside/hangar'
                  // required parameter may not be specified but checked later as 404
                  final String firstElement = Srl.substringFirstFront(paramPath, "/"); // e.g. sea (from sea/dockside)
                  if (firstElement.equals(mappingMethodName)) { // e.g. sea(first) with sea/dockside
                      final int paramCount = Srl.count(Srl.trim(paramPath, "/"), "/"); // e.g. sea/dockside => 1
                      return determineOptionalPath(paramPath, paramCount, /*namedMethod*/true);
                  }
                  return HandledOptionalPath.MAYBE_UNMATCHES; // might be certainly unmatches, for compatible
              }
          } else {
              return HandledOptionalPath.NON_OPTIONAL;
          }
      }
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