Activitity Method Parameter and Return Value Not Retaining State

Developer Corner
1

Hello
I have a simple workflow with Couple of activities
First Activity is fetching data from downsteam system using REST API
then it adding few more addition properties
and then return that value

@Data
class DownstreamFirstActivityMethodResponse implements Serializable {
//serial version id included here

private String prop1;
private String prop2;
/**/
private String firstActivityMethodSettingAsAdditionalParam;

}

class FirstActivityParam implements Serializable {
//serial version id included here
private String workflowIsSetting;
private String firstActivityMethodSettingAsReturnParam;
}

Signature of the first activity:
________________________________
    DownstreamFirstActivityMethodResponse firstActivityMethod(FirstActivityParam param)
    
    Note: firstActivityMethod does 3 things
    1) param.setFirstActivityMethodSettingValueAsReturnParam("first activity setting value")
    2) Calls REST API and result of downstream is an instance of DownstreamFirstActivityMethodResponse
    3) sets a new prop - 
    downstreamFirstActivityMethodResponse.setFirstActivityMethodSettingAsAdditionalParam("THIS IS NEW PROP VALUE SET BY 1st ACTIVYT");
    
    
    
    
Signature of the second activity:
---------------------------------
    void secondActivityMethod(FirstActivityParam param, DownstreamFirstActivityMethodResponse input )



    workflow logic - inside workflow method:
    --------------------------------------
    
    FirstActivityParam param = new FirstActivityParam();
         param.setWorkflowIsSetting("somevalue");

    DownstreamFirstActivityMethodResponse firstActityReturnValue = firstactivity.firstActivityMethod(param);

    System.out.println(firstActityReturnValue.getFirstActivityMethodSettingAsReturnParam());
          //Expected : THIS IS NEW PROP VALUE SET BY 1st ACTIVYT
          //BUT - is NULL
    
    System.out.println(FirstActivityParam.getFirstActivityMethodSettingValue());
          //Expected : "first activity setting value"
          //BUT - is NULL
          
           
    secondActivityObject.secondActivityMethod(param,firstActityReturnValue)
    //2nd Activity Needs those additional return param value and addional prop value from downstreamResponse
    
    
Question : it s really a puzzle for me to see that, after 1stActivityMethod call completion - those addional elements are nullfied, why