KeyError: 'traitsui.toolkits'

Traceback (most recent call last):
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/importlib_metadata/__init__.py", line 289, in __getitem__
return next(iter(self.select(name=name)))
StopIteration

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/home/ubuntu/zhangweili/DAIR-V2X-main/tools/visualize/vis_label_in_3d.py", line 3, in
import mayavi.mlab as mlab
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/mayavi/mlab.py", line 16, in
from mayavi.tools.camera import view, roll, yaw, pitch, move
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/mayavi/tools/camera.py", line 24, in
from .engine_manager import get_engine
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/mayavi/tools/engine_manager.py", line 13, in
from mayavi.preferences.api import preference_manager
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/mayavi/preferences/api.py", line 4, in
from .preference_manager import preference_manager
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/mayavi/preferences/preference_manager.py", line 29, in
from traitsui.api import View, Group, Item
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/traitsui/api.py", line 256, in
from .editors.api import ArrayEditor
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/traitsui/editors/__init__.py", line 16, in
from .api import ArrayEditor
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/traitsui/editors/api.py", line 86, in
from .code_editor import CodeEditor
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/traitsui/editors/code_editor.py", line 21, in
class CodeEditor(EditorFactory):
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/traitsui/editors/code_editor.py", line 33, in CodeEditor
mark_color = Color(0xECE9D8)
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/traits/trait_factory.py", line 40, in __call__
return self.maker_function(*args, **metadata)
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/traitsui/toolkit_traits.py", line 43, in ColorTrait
return toolkit().color_trait(*args, **traits)
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/traitsui/toolkit.py", line 110, in toolkit
_toolkit = find_toolkit("traitsui.toolkits")
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/pyface/base_toolkit.py", line 285, in find_toolkit
plugin for plugin in importlib_metadata.entry_points()[entry_point]
File "/home/ubuntu/anaconda3/envs/dair_v2x/lib/python3.7/site-packages/importlib_metadata/__init__.py", line 291, in __getitem__
raise KeyError(name)
KeyError: 'traitsui.toolkits'
mayavi==4.8.1,traitsui==7.2.1, traits==6.2.0, traitlets==5.9.0, importlib_metadata==6.0.0, importlib_resources==5.12.0
What is the reason for this, and how to solve it? Thanks!