code: public <TTDPO> TransformedDataProviderContext transform(Transformer<TDPO, TTDPO> ruleInputTransformer) {
          if (ruleInputTransformer != null) {
              addedRuleInputTransformers.add(ruleInputTransformer);
          }
  
          // Change context because output type has changed
          return new TransformedDataProviderContext<DPO, TTDPO>(addedTriggers, addedDataProviders,
                  dataProviderToRuleMapping, addedRuleInputTransformers);
      }
docs: Adds the specified rule input transformer to the validator under construction.
  
  @param ruleInputTransformer Rule input transformer to be added.
  @param <TTDPO>              Type of transformer output.
  
  @return Context allowing further construction of the validator using the DSL.