docs: protected final FluentModelTImpl prepareInlineDefine(String name, String key) {
          if (find(key) != null) {
              throw new IllegalArgumentException("A child resource ('" + childResourceName + "') with name (key) '" + name + " (" + key + ")' already exists");
          }
          FluentModelTImpl childResource = newChildResource(name);
          childResource.setPendingOperation(ExternalChildResourceImpl.PendingOperation.ToBeCreated);
          return super.prepareForFutureCommitOrPostRun(childResource);
      }