Simplify 'is null' check

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers/Lightup/LightupHelpers.cs

@@ -232,7 +232,7 @@ internal static Func<TSyntax, SeparatedSyntaxListWrapper<TProperty>, TSyntax> Cr
                         throw new NullReferenceException();
                     }
 
-                    if (ReferenceEquals(newValue, null))
+                    if (newValue is null)
                     {
                         return syntax;
                     }