title: Foreign Key Reference Already Has Value Exception Linq to SQL When Assigning Null
body: <p>In the case where a foreign key already has a reference but I want to remove that reference how would I do that? </p>
  
  <pre><code>queryRecord.Single().OrderID = null;
  </code></pre>
  
  <p>Throws this ForeignKeyReferenceAlreadyHasValueException, I realize you have to set it to an entity, but how can I set it to a null entity?</p>
  
  <p>I tried</p>
  
  <pre><code>Order nullOrder = new Order();
  queryRecord.Single().Orders = nullOrder.OrderID;
  </code></pre>
  
  <p>but that also throws the same ForeignKeyReferenceAlreadyHasValueException</p>
  
  <p>So how do I null that field?</p>