C#

new SomeClass() is the syntax to instantiate a class in C#. However, new Guid() does not generate a new GUID. It instead returns an empty GUID. If you intend to use an empty GUID, consider using Guid.Empty as it is more straightforward to comprehend. If you wish to generate a new usable GUID, consider using Guid.NewGuid().

The ToString method should return a string that best represents your class/object. Returning null from such a method does not make any sense and is therefore recommended that you refactor this method to return a more suitable and appropriate representation.

Obsolete attribute allows you to mark certain entities as obsolete, thereby discouraging users from using them. However, to convey the full context, it is recommended that you specify the obsolete-message/description. Failing to do so produces a blank line/empty string during the build process and can cause confusion.

While converting strings to lower/upper case and then comparing might work to perform a case insensitive comparison, the safer, reliable, and performant alternative is to invoke the string.Equals method while specifying the StringComparison.OrdinalIgnoreCase enum.

Individual elements in a string or an array can be accessed via the bracketed expression. The norm for accessing elements from last is usually in the format of foo[ub - i] where ub is the upper bound and i is an index. This expression however can be simplified and rewritten as foo[^i].