The error specifically indicates that undefined variable or class name: workflowAssignment This could mean it wasn't initialized properly. Try the below code to verify the same. 

if (workflowAssignment != null) {
    LogUtil.info("Value of workflowAssignment : ", workflowAssignment.toString());
} else {
    LogUtil.info("workflowAssignment is null","");
}

Additionally check if you have imported the necessary package

import org.joget.workflow.model.WorkflowAssignment;

Let us know if this works. Please share your full beanshell script if possible for further debugging. 

I checked the same code in a tool and not inside a route bean. It works there. So it seems, that workflowassignment is not propagated to the route bean but only to a tool bean.

I cannot think of any reason why this should be a feature and not a bug.

Anyway by splitting the code into a tool and a route it is possible to work around it.

and here now the two scripts:

This is working:

Route A has a transition to Tool B.

Bean in Route A

import org.joget.workflow.model.DecisionResult;
import org.joget.commons.util.LogUtil;
import org.joget.workflow.model.service.*;


String groupsRequested = "#form.account_signup.groupsRequested#";
int groupsRequestedArraySize;
String[] groupsRequestedArray = groupsRequested.split(";");

if (groupsRequested != "") {
    groupsRequestedArraySize = groupsRequestedArray.length;
} else {
    groupsRequestedArraySize = 0;
}

int groupCounter = Integer.valueOf("#variable.groupCounter#");


//LogUtil.info("Value of groupCounter             : ", "" + groupCounter);
//LogUtil.info("Value of groupsRequested          : ", groupsRequested);
//LogUtil.info("Value of groupsRequestedArray     : ", Arrays.toString(groupsRequestedArray));
//LogUtil.info("Value of groupsRequestedArraySize : ", "" + groupsRequestedArraySize);


DecisionResult result = new DecisionResult();
 
if (groupCounter >= groupsRequestedArraySize ) {
    result.addTransition("noGroupUpdate");
//    LogUtil.info("Value of Transition             : ", "noGroupUpdate");
    
} else {
    result.addTransition("groupUpdate");
//    LogUtil.info("Value of Transition             : ", "groupUpdate");
}
 
result.setIsAndSplit(true);
 
return result;

Bean in Tool B

import org.joget.commons.util.LogUtil;
import org.joget.workflow.model.service.*;


String groupsRequested = "#form.account_signup.groupsRequested#";

String[] groupsRequestedArray = groupsRequested.split(";");

int groupCounter = Integer.valueOf("#variable.groupCounter#");

//LogUtil.info("Value of groupCounter             : ", "" + groupCounter);
//LogUtil.info("Value of groupsRequestedArray     : ", Arrays.toString(groupsRequestedArray));
//LogUtil.info("Value of workflowAssignment       : ", workflowAssignment.toString());

String group = groupsRequestedArray[groupCounter++];

WorkflowManager wm = (WorkflowManager) pluginManager.getBean("workflowManager");
wm.activityVariable(workflowAssignment.getActivityId(),"group", group);
wm.activityVariable(workflowAssignment.getActivityId(),"groupCounter", String.valueOf(groupCounter));

//LogUtil.info("Value of groupCounter             : ", "" + groupCounter);
//LogUtil.info("Value of group                    : ", "" + group);

This is not working:

All code is in the Bean for Route A, not Tool B.

import org.joget.workflow.model.DecisionResult;
import org.joget.commons.util.LogUtil;
import org.joget.workflow.model.service.*;

String groupsRequested = "#form.account_signup.groupsRequested#";
int groupsRequestedArraySize;

int groupCounter = Integer.valueOf("#variable.groupCounter#");

String[] groupsRequestedArray = groupsRequested.split(";");

String group = groupsRequestedArray[groupCounter++];

WorkflowManager wm = (WorkflowManager) pluginManager.getBean("workflowManager");

wm.activityVariable(workflowAssignment.getActivityId(),"group", group);

// This line above throws already error since workflowAssignment is null

wm.activityVariable(workflowAssignment.getActivityId(),"groupCounter", String.valueOf(groupCounter));

if (groupsRequested != "") {
    groupsRequestedArraySize = groupsRequestedArray.length;
} else {
    groupsRequestedArraySize = 0;
}

int groupCounter = Integer.valueOf("#variable.groupCounter#");

//LogUtil.info("Value of groupCounter             : ", "" + groupCounter);
//LogUtil.info("Value of groupsRequested          : ", groupsRequested);
//LogUtil.info("Value of groupsRequestedArray     : ", Arrays.toString(groupsRequestedArray));
//LogUtil.info("Value of groupsRequestedArraySize : ", "" + groupsRequestedArraySize);

DecisionResult result = new DecisionResult();
 
if (groupCounter >= groupsRequestedArraySize ) {
    result.addTransition("noGroupUpdate");
//    LogUtil.info("Value of Transition             : ", "noGroupUpdate");
    
} else {
    result.addTransition("groupUpdate");
//    LogUtil.info("Value of Transition             : ", "groupUpdate");
}
 
result.setIsAndSplit(true);
 
return result;