code: protected RealJsonEngine createDefaultJsonEngine() {
          final JsonEngineResource resource = new JsonEngineResource();
          mappingOption.ifPresent(op -> {
              resource.acceptMappingOption(op);
          });
          yourEngineCreator.ifPresent(creator -> {
              resource.useYourEngineCreator(creator);
          });
          return createGsonJsonEngine(resource);
      }
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