code: protected void mappingJsonBody(ActionRuntime runtime, VirtualForm virtualForm, String json) {
          final JsonManager jsonManager = getJsonManager();
          try {
              final Class<?> formType = virtualForm.getFormMeta().getRootFormType(); // called only when root here
              final Object fromJson = jsonManager.fromJson(json, formType);
              acceptJsonRealForm(virtualForm, fromJson);
          } catch (RuntimeException e) {
              throwJsonBodyParseFailureException(runtime, virtualForm, json, e);
          }
      }
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