code: public B camundaInBusinessKey(String businessKey) {
      CamundaIn param = modelInstance.newInstance(CamundaIn.class);
  
      param.setCamundaBusinessKey(businessKey);
  
      addExtensionElement(param);
  
      return myself;
    }
docs: Sets a "camunda:in" parameter to pass the business key from the signal-throwing
  process instance to the signal-catching process instance
  
  @param businessKey the business key string or expression of the signal-throwing process instance
  @return the builder object