Hi ,
 I have this code below. I need to add values to Map<Id,List<Id>>, it is giving an error , can anyone pleas ehelp?


trigger Project_Risk_Review_Trigger on Project_Risk_Review__c (after insert,after update) {
   
   
         // Create a new list of sharing objects for Project_Risk_Review
         List<Project_Risk_Review__Share> ProjectRiskReviewShrs  = new List<Project_Risk_Review__Share>();

         Map<Id,List<Id>> OldSharesMap=new Map<Id,List<Id>>();
         // Declare variables for super user sharing.
         Project_Risk_Review__Share SuperUserShrDvp;
         Project_Risk_Review__Share SuperUserShrDelegate;
         Project_Risk_Review__Share SuperUserShrProjectDirector;
         Project_Risk_Review__Share SuperUserShrChairReviewer;
         for(Project_Risk_Review__c NewAssessment : trigger.new){
                  
                  Project_Risk_Review__c oldReview = Trigger.oldMap.get(NewAssessment.ID);                  
                  if(NewAssessment.DVP__c != Null && ((Trigger.IsInsert && Trigger.IsAfter)||(Trigger.IsUpdate && Trigger.IsAfter && (NewAssessment.DVP__c !=oldReview.DVP__c)))){
                      // Instantiate the sharing objects
                      SuperUserShrDvp = new Project_Risk_Review__Share();
                      // Set the ID of record being shared
                      SuperUserShrDvp.ParentId = NewAssessment.Id;
                      // Set the ID of user or group being granted access
                      SuperUserShrDvp.UserOrGroupId =NewAssessment.DVP__c;
                      SuperUserShrDvp.AccessLevel = 'edit';
                      // Set the Apex sharing reason for DVP
                      SuperUserShrDvp.RowCause = Schema.Project_Risk_Review__Share.RowCause.PRAS_Super_Users_R_W_Access__c;
                      // Add objects to list for insert
                      ProjectRiskReviewShrs.add(SuperUserShrDvp);
                      if(Trigger.IsAfter && Trigger.IsUpdate){
                        OldSharesMap.put(oldReview.ID,oldReview.DVP__c);
                      }
                  }