docs: public static Collection<DimensionSpec> extractionsToRewrite(GroupByQuery query)
    {
      return Collections2.filter(
          query.getDimensions(), new Predicate<DimensionSpec>()
          {
            @Override
            public boolean apply(DimensionSpec input)
            {
              return input.getExtractionFn() != null
                     && ExtractionFn.ExtractionType.ONE_TO_ONE.equals(
                  input.getExtractionFn().getExtractionType()
              );
            }
          }
      );
    }