Added ALTER Support for Null Type Tables

Why it matters

This feature allows users to perform ALTER operations on Null tables, which previously did not support schema changes. It enables better schema management and consistency for Null tables, improving user control and flexibility when working with this special table engine.

How to use it

Use the ALTER statement with tables of the Null engine as you would with other tables. For example, you can add or drop columns or modify table structure on Null tables using the standard ALTER TABLE syntax.