Add a case when CType migration has not been done (#188)

* Add a case when CType migration has not been done

* Update Documentation/Exceptions/1540246570.rst

Co-authored-by: Garvin Hicking <[email protected]>

* Update Documentation/Exceptions/1540246570.rst

Co-authored-by: Garvin Hicking <[email protected]>

* Update 1540246570.rst

---------

Co-authored-by: Lina Wolf <[email protected]>
Co-authored-by: Garvin Hicking <[email protected]>

Author: 3 people

Documentation/Exceptions/1540246570.rst

@@ -126,3 +126,17 @@ The error does not occur when you use the Fluid lanuage tag with a path:
 ..  code-block:: xml
 
     <f:translate key = "LLL:EXT:yourExtension/Resources/Private/Language/locallang.xml:Button_Helpful" />
+
+TYPO3 12/13 - General Plugin: No Content Object definition found at TypoScript object path "tt_content.list.20"
+==============================================================================================================
+
+This exception could happen because a plugin was registered before using the :php:`list` content element 
+and the plugin subtype :php:`list_type` and is now registered as :php:`ExtensionUtility::PLUGIN_TYPE_CONTENT_ELEMENT`.
+
+Have a look at `Deprecation: #105076 - Plugin content element and plugin sub types <https://docs.typo3.org/permalink/changelog:deprecation-105076-1726923626>`_.
+
+Either an Upgrade Wizard was not executed for those plugins or may be you need to create one.
+
+If Upgrade Wizard creation is required, you can have a look in TYPO3 core for example, search 
+Upgrade Wizard extending :php:`AbstractListTypeToCTypeUpdate`, like :php:`final class IndexedSearchCTypeMigration extends AbstractListTypeToCTypeUpdate`.
+