My question is continuation of what I have asked [here][1]


  [1]: http://salesforce.stackexchange.com/questions/116478/how-to-define-a-map-with-id-and-listcase-of-records

How do I replace from:

    parentChildCase.get(cMap.get(c).ID).add(cMap.get(c));

to this Id (`pId`):

    Map<id, id> par = new Map<id, id>();  
    
    List <case> rcases =[SELECT ... FROM CASE WHERE <other_conditions....>];
    for (case c : rcases) {
      par.put(c.id,c.ParentId);
    }

    Id = pId = par.get(cMap.get(c).Parentid); 

Error `NullPointerException: Attempt to de-Reference a null object`

    for(ID c : cMap.keySet()) 
    {
        if(parentChildCase.containsKey(cMap.get(c).ID)) 
        {
            //parentChildCase.get(cMap.get(c).ID).add(cMap.get(c));
            Id pId = par.get(cMap.get(c).Parentid);
            parentChildCase.get(pId).add(cMap.get(c)); //ERROR      NullPointerException: Attempt to de-Reference a null object
        }
        else
        {
            List<Case> cases = new List<Case>();
            cases.add(cMap.get(c));
            parentChildCase.put(cMap.get(c).ID, cases);
        }
    }