Parallel LINQ (PLINQ) Thread Safety - Using AsParallel + List<T>.Add() Returns Object Reference Not Set to an Instance of an Object 1. June 2015 DeanMay@phidiax.com Phidiax Technology, .Net (0) PLINQ (Parallel LINQ) for large data operations to automate threading returns "Object Reference Not Set to an Instance of an Object" due to Thread Safety if not using ConcurrentBag. [More]