using Uniqueidentifier data type in katalon

Request datatype was uniqueidentifier
Katalon there is no similar format to cast for the datatype.
Iam using parameter as Variables.
{

“WorkflowId”:"${WorkflowId}",

}

in the variable i defined as workflowid as String. As there is no matching data type for the unique identifier.

System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Controllers.ExceptionFilterResult.d__0.MoveNext(). Error: Error converting value “” to type ‘System.Guid’. Path ‘WorkflowId’. - Could not cast or convert from System.String to System.Guid.