code: public EntityDescriptor extractEntityDescriptor(HeuristicConfigPolicy configPolicy) {
          if (entityClass != null) {
              SolutionDescriptor solutionDescriptor = configPolicy.getSolutionDescriptor();
              EntityDescriptor entityDescriptor = solutionDescriptor.getEntityDescriptorStrict(entityClass);
              if (entityDescriptor == null) {
                  throw new IllegalArgumentException("The selectorConfig (" + this
                          + ") has an entityClass (" + entityClass + ") that is not a known planning entity.\n"
                          + "Check your solver configuration. If that class (" + entityClass.getSimpleName()
                          + ") is not in the entityClassSet (" + solutionDescriptor.getEntityClassSet()
                          + "), check your " + PlanningSolution.class.getSimpleName()
                          + " implementation's annotated methods too.");
              }
              return entityDescriptor;
          } else if (mimicSelectorRef != null) {
              return configPolicy.getEntityMimicRecorder(mimicSelectorRef).getEntityDescriptor();
          } else {
              return null;
          }
      }
docs: ************************************************************************