code: @Override
      protected ImmutableMap<Class<? extends QueryOptimizationProposal>, Class<? extends ProposalExecutor>>
      generateOptimizationConfigurationMap() {
          return Stream.concat(
                      super.generateOptimizationConfigurationMap().entrySet().stream(),
                      systemConfiguration.generateOptimizationConfigurationMap().entrySet().stream())
                  .distinct()
                  .collect(ImmutableCollectors.toMap());
      }
docs: Can be overloaded by sub-classes