docs: protected final FluentModelTImpl prepareInlineDefine(FluentModelTImpl model) {
          FluentModelTImpl childResource = find(model.childResourceKey());
          if (childResource != null) {
              throw new IllegalArgumentException(pendingOperationMessage(model.name(), model.childResourceKey()));
          }
          model.setPendingOperation(ExternalChildResourceImpl.PendingOperation.ToBeCreated);
          this.childCollection.put(model.childResourceKey(), model);
          return super.prepareForFutureCommitOrPostRun(model);
      }