A Data Manager. It allows you to store, query and get key/value paired information specific to this Game Object. null by default. Automatically created if you use getData or setData or setDataEnabled .
So null seems correct.
If you want the class members, try logging without .data.
This, specifically, is the part of the documentation that’s significant here. If you want to use Phaser’s built-in data manager, use getData and setData on the sprite instead of accessing data directly.