is it possible to populate subclass of FieldItemList from code? The context first: 

I'm migrating a website from D7 to D8 and one of the modules has no update on D8.
I found an alternate module with the same functionality. 

For the FieldType of the alternate module, it consists in a subclassOf FieldItemList, lets say MyFieldItemList and a subclass of FieldItemBase, lets say MyFieldItemBase.

I'm quite stuck on this:


I exported the data from D7 using views and a csv generation export
I'm creating a micro Drupal 8 module to upload csv file and populate existing nodes with csv data
I can get the subclass of FieldItemList from my node and saw the "append(...)" method in documentation.
I can't manage to find how to create a new item of type MyFieldItemBase


I can't find any examples in existing modules and over the web, is there a flaw in the import process I wanted to follow?
So I found out what I was trying to do in a complicated way could be done by simply setting the field values on the node, like this:

            $node-&gt;set($field_name, $field_values);
            $node-&gt;save();