code: public void setDummyFactory(final DummyFactory dummyFactory) {
          if (entities.size() > 0) {
              throw new IllegalStateException("The dummy factory cannot be changed after an entity was generated!");
          }
          if (dummyFactory == null) {
              this.dummyFactory = new DefaultDummyFactory();
          } else {
              this.dummyFactory = dummyFactory;
          }
      }
docs: Sets the new dummy factory, that will be used to generate dummy entities from now on. Changing this does not affect old dummy entities.
  Must not be called after entities are created or an {@link IllegalStateException} gets thrown.
  
  @param dummyFactory The new dummy factory. If {@code null}, a {@link DefaultDummyFactory} gets used.