Crm 2011 + To provide reference target dynamically in a custom workflow

Hi ,

I have created a custom workflow to assign multiple records to a Team

i am providing 2 input parameters -
1)FetchXml

2)Custom parameter

Basically i want to fetch all the records related to the primary entity.Foreg my entity name is "new_abc" and other entity is "new_xyz". i want to fetch all the records "new_abc" records that are related to "new_xyz".
I have a look up of "new_xyz" on my primary entity.

But i am not understanding why the primaryid is not getting set. it is throwing me error.
Please if anybody could help me in this.it will be a great help

Below is my code for the custom workflow -

public class Fetch : CodeActivity
    {
        [Input("Fetch XML")]
        public InArgument<string> FetchXML { get; set; }

        [Input("Team")]
        [ReferenceTarget("team")]
        public InArgument<EntityReference> Team { get; set; }

        [Input("Entity Logical Name")]
        public InArgument<string> EntityName { get; set; }

        [Input("Attribute Name Input")]
        public InArgument<string> AttributeName { get; set; }

        protected override void Execute(CodeActivityContext executionContext)
        {
            try
            {
                IWorkflowContext context = executionContext.GetExtension<IWorkflowContext>();
                IOrganizationServiceFactory serviceFactory = executionContext.GetExtension<IOrganizationServiceFactory>();
                IOrganizationService service = serviceFactory.CreateOrganizationService(context.UserId);
                ITracingService tracer = executionContext.GetExtension<ITracingService>();

                RowReturned.Set(executionContext, false);

                Guid primaryId = Guid.Empty;



                //To get Attribute from workflow
                string attribute = AttributeName.Get(executionContext);
                string entityName = EntityName.Get(executionContext);


                //Creating entity of given type
                Entity entity = new Entity(entityName);


                EntityReference entityReference = (EntityReference)entity.GetAttributeValue<EntityReference>(attribute);
                primaryId = entityReference.Id;


                string fetch = FetchXML.Get<string>(executionContext);
                fetch = String.Format(fetch, primaryId);

                EntityCollection recordlist = service.RetrieveMultiple(new FetchExpression(fetch));

                Count.Set(executionContext, recordlist.Entities.Count);

                if (recordlist.Entities.Count > 0)
                {
                    foreach (Entity item in recordlist.Entities)
                    {
                        // Create the Request Object and Set the Request Object's Properties
                        var request = new AssignRequest
                        {
                            Assignee = new EntityReference("team", Team.Get<EntityReference>(executionContext).Id),
                            Target = new EntityReference("mcg_locationaddress", item.Id)
                        };

                        // Execute the Request
                        service.Execute(request);
                    }

                }
            }
            catch (Exception ex)
            {
                Helpers.Throw(String.Format("An error occurred in the {0} plug-in.",
                        this.GetType().ToString()),
                      ex);
            }


        } 

Thanks,