Comparing value types with null is evil and eats babies.
http://tirania.org/blog/archive/2007/Mar-13-1.html

Such comparison is present in Ruby.Compiler.AST.AliasStatement.cs.

Date: 2007-09-03 03:24
Sender: John Messerly

Thanks Seo. I removed the useless Debug.Assert that was comparing
SymbolId to null.