[TASK] Allow NULL for TCA type "json" fields

When using TCA type "json", corresponding database
column is automatically generated - if not already
defined. This column is now configured as nullable
to prevent SQL errors in case no default value has
been defined.

Resolves: #100156
Related: #100154
Related: #100101
Related: #100088
Releases: main
Change-Id: Ib9f6f17d33ed2af8f5b2128a68cb16d438feb22b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78109


Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Jochen <rothjochen@gmail.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Jochen <rothjochen@gmail.com>

typo3/sysext/core/Classes/Database/Schema/DefaultTcaSchema.php

@@ -517,7 +517,7 @@ class DefaultTcaSchema
                     $this->quote($fieldName),
                     'json',
                     [
-                        'notnull' => true,
+                        'notnull' => false,
                     ]
                 );
             }