The == overload in the Oid class is incorrect. In the case that one of the Oids in a comparison is null, an exception is thrown. The overload does not take into account the possibility that either reference is null.

This is what the overload should look like:

public static bool operator ==(Oid a, Oid b){

// Return true if both are same instance or both are null
if (System.Object.ReferenceEquals(a, b))

{ return true; }

// Return false if only one instance is null
if (((object)a == null) || ((object)b == null))

{ return false; }

return a.Equals(b);
}

This is taken from the following MS site:

http://msdn.microsoft.com/en-us/library/ms173147%28VS.80%29.aspx