[Bug][Mac]: unsupported operand type(s) for +: 'NoneType' and 'float'

[guotong1988]

Bug Description

try to run advanced_hybrid_robot.py on MacBook [CPU]

Steps to Reproduce

import numpy as np
import genesis as gs


########################## init ##########################
gs.init(seed=0, precision="32", logging_level="debug")

######################## create a scene ##########################
dt = 3e-3
scene = gs.Scene(
    sim_options=gs.options.SimOptions(
        substeps=10,
    ),
    viewer_options=gs.options.ViewerOptions(
        camera_pos=(1.5, 1.3, 0.5),
        camera_lookat=(0.0, 0.0, 0.0),
        camera_fov=40,
    ),
    rigid_options=gs.options.RigidOptions(
        dt=dt,
        gravity=(0, 0, -9.8),
        enable_collision=True,
        enable_self_collision=False,
    ),
    mpm_options=gs.options.MPMOptions(
        dt=dt,
        lower_bound=(0.0, 0.0, -0.2),
        upper_bound=(1.0, 1.0, 1.0),
        gravity=(0, 0, 0),  # mimic gravity compensation
        enable_CPIC=True,
    ),
    vis_options=gs.options.VisOptions(
        show_world_frame=True,
        visualize_mpm_boundary=False,
    ),
)

########################## entities ##########################
scene.add_entity(morph=gs.morphs.Plane())

robot = scene.add_entity(
    morph=gs.morphs.URDF(
        file="urdf/simple/two_link_arm.urdf",
        pos=(0.5, 0.5, 0.3),
        euler=(0.0, 0.0, 0.0),
        scale=0.2,
        fixed=True,
    ),
    material=gs.materials.Hybrid(
        mat_rigid=gs.materials.Rigid(
            gravity_compensation=1.0,
        ),
        mat_soft=gs.materials.MPM.Muscle(  # to allow setting group
            E=1e4,
            nu=0.45,
            rho=1000.0,
            model="neohooken",
        ),
        thickness=0.05,
        damping=1000.0,
    ),
)

ball = scene.add_entity(
    morph=gs.morphs.Sphere(
        pos=(0.8, 0.6, 0.1),
        radius=0.1,
    ),
    material=gs.materials.Rigid(rho=1000, friction=0.5),
)

########################## build ##########################
scene.build()

########################## run ##########################



def run_sim(scene, robot):
    scene.reset()
    for i in range(1000):
        dofs_ctrl = np.array(
            [
                1.0 * np.sin(2 * np.pi * i * 0.001),
            ]
            * robot.n_dofs
        )

        robot.control_dofs_velocity(dofs_ctrl)

        scene.step()

gs.tools.run_in_another_thread(fn=run_sim, args=(scene, robot))
scene.viewer.start()

Relevant log output

Traceback (most recent call last):
  File "/Users/guotong/Downloads/Genesis-0.2.1/examples/tutorials/advanced_hybrid_robot.py", line 41, in <module>
    robot = scene.add_entity(
            ^^^^^^^^^^^^^^^^^
  File "/Users/guotong/Downloads/Genesis-0.2.1/genesis/utils/misc.py", line 38, in wrapper
    return method(self, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/guotong/Downloads/Genesis-0.2.1/genesis/engine/scene.py", line 359, in add_entity
    entity = self._sim._add_entity(morph, material, surface, visualize_contact)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/guotong/Downloads/Genesis-0.2.1/genesis/engine/simulator.py", line 149, in _add_entity
    entity = HybridEntity(
             ^^^^^^^^^^^^^
  File "/Users/guotong/Downloads/Genesis-0.2.1/genesis/engine/entities/hybrid_entity.py", line 70, in __init__
    part_soft = func_instantiate_soft_from_rigid(
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/guotong/Downloads/Genesis-0.2.1/genesis/engine/entities/hybrid_entity.py", line 427, in default_func_instantiate_soft_from_rigid
    part_soft = scene.add_entity(
                ^^^^^^^^^^^^^^^^^
  File "/Users/guotong/Downloads/Genesis-0.2.1/genesis/utils/misc.py", line 38, in wrapper
    return method(self, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/guotong/Downloads/Genesis-0.2.1/genesis/engine/scene.py", line 359, in add_entity
    entity = self._sim._add_entity(morph, material, surface, visualize_contact)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/guotong/Downloads/Genesis-0.2.1/genesis/engine/simulator.py", line 137, in _add_entity
    entity = self.mpm_solver.add_entity(self.n_entities, material, morph, surface)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/guotong/Downloads/Genesis-0.2.1/genesis/engine/solvers/mpm_solver.py", line 213, in add_entity
    entity = MPMEntity(
             ^^^^^^^^^^
  File "/Users/guotong/Downloads/Genesis-0.2.1/genesis/engine/entities/mpm_entity.py", line 26, in __init__
    super().__init__(
  File "/Users/guotong/Downloads/Genesis-0.2.1/genesis/engine/entities/particle_entity.py", line 69, in __init__
    self.sample()
  File "/Users/guotong/Downloads/Genesis-0.2.1/genesis/engine/entities/particle_entity.py", line 181, in sample
    particles_i += np.array(morph_i.pos)
TypeError: unsupported operand type(s) for +: 'NoneType' and 'float'
[Genesis] [20:48:38] [INFO] 💤 Exiting Genesis and caching compiled kernels...

Environment

• OS: Apple M3 Pro
• CPU

Release version or Commit ID

tag v0.2.1