Help with Rigidification

Hello everyone!
I am trying to run the Rigidify function example that @damien-marchaluniv-lille1-fr posted in this other topic: https://www.sofa-framework.org/community/forum/topic/rigidmapping-from-rigid3d-to-only-some-particles-of-fembody/
The example is the following one:

def createScene(rootNode):
        """
        """
        from stlib.scene import MainHeader
        from stlib.physics.deformable import ElasticMaterialObject
        from stlib.physics.mixedmaterial import Rigidify
        from splib.objectmodel import setData

        MainHeader(rootNode, plugins=["SofaSparseSolver"])
        rootNode.VisualStyle.displayFlags = "showBehavior"

        modelNode = rootNode.createChild("Modeling")
        elasticobject = ElasticMaterialObject(modelNode, "mesh/liver.msh", "ElasticMaterialObject")

        # Rigidification of the elasticobject for given indices with given frameOrientations.
        o = Rigidify(modelNode,
        elasticobject,
        name="RigidifiedStructure",
        frames=[[0., 0., 0], [0., 0., 0]],
        groupIndices=[[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10], [48, 49, 50, 51]])

        # Activate some rendering on the rigidified object.
        setData(o.RigidParts.dofs, showObject=True, showObjectScale=1, drawMode=2)
        setData(o.RigidParts.RigidifiedParticules.dofs, showObject=True, showObjectScale=0.1,
        drawMode=1, showColor=[1., 1., 0., 1.])
        setData(o.DeformableParts.dofs, showObject=True, showObjectScale=0.1, drawMode=2)
        o.RigidParts.createObject("FixedConstraint", indices=0)

        simulationNode = rootNode.createChild("Simulation")
        simulationNode.createObject("EulerImplicitSolver")
        simulationNode.createObject("CGLinearSolver")
        simulationNode.addChild(o)
        return rootNode

The problem is that when I try to run this example from Sofa, the next error appear in the terminal:

ModuleNotFoundError: No module named 'stlib'

At:
  example.py(4): createScene

I do not know why I get this error, I have the STLIB plugin installed (because I have the v20.12.03 binaries version of Sofa, and STLIB is supposed to be included in the binaries).
I would appreciate any help. Thanks in advance.

Cheers,
Sergio.