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 /*error: System.NullPointerException: Attempt to de-reference a null object 
Class.UserAccessDetailsController.getObjectLabels: line 290, column 1
line 290 is this describe.get(op.SObjectType).getDescribe().getLabel()));
*/

 public List<NameLabel> getObjectLabels() {
        if (null == xObjectLabels) {
            List<NameLabel> result = new List<NameLabel>();
            Map<String,SObjectType> describe = Schema.getGlobalDescribe();

            
            for (ObjectPermissions op : [SELECT SObjectType FROM ObjectPermissions 
                                          WHERE Parent.Profile.Name = 'System Administrator'  ]) {
                result.add(new NameLabel(op.SObjectType, 
                                         describe.get(op.SObjectType).getDescribe().getLabel()));
            }
            result.sort();
            xObjectLabels = result;
        }
        return xObjectLabels;
    }