This builder builds the block type that is used by default in BlockBuilder#build This builder does not offer any special properties to set, you can only build it.
This class was added by a mod with mod-id
contenttweaker. So you need to have this mod installed if you want to use this feature.
Importing the class
It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import at the very top of the file.