fix: add proper comment for MariaDB fix

Signed-off-by: mertmit <mertmit99@gmail.com>

packages/nocodb/src/lib/db/sql-client/lib/mysql/MysqlClient.ts

@@ -671,6 +671,11 @@ class MysqlClient extends KnexClient {
             column.cdf = response[0][i].cdf;
           }
 
+          // Reference: https://github.com/nocodb/nocodb/issues/4625
+          // There is an information_schema difference on MariaDB and MySQL
+          // while MySQL keeps NULL as default value if no value provided
+          // MariaDB keeps NULL as string (if you provide a string NULL it is wrapped by single-quotes)
+          // so we check if database is MariaDB and if so we convert the string NULL to null
           if (this._version?.version) {
             if (this._version.version.includes('Maria')) {
               if (column.cdf === 'NULL') {