Fix: add check for JsonModel

[yufansong]

When I try python examples/minimalist_demo.py will meet error. The key reason should be forget the config value in redis. Add some check for better error prompt.

The following is the error bug

    https://beartype.readthedocs.io/en/latest/api_roar/#pep-585-deprecations
  warn(
Traceback (most recent call last):
  File "/home/yufansong/sotopia/examples/minimalist_demo.py", line 27, in <module>
    asyncio.run(
  File "/home/yufansong/miniconda3/envs/bridge/lib/python3.11/asyncio/runners.py", line 190, in run
    return runner.run(main)
           ^^^^^^^^^^^^^^^^
  File "/home/yufansong/miniconda3/envs/bridge/lib/python3.11/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/yufansong/miniconda3/envs/bridge/lib/python3.11/asyncio/base_events.py", line 654, in run_until_complete
    return future.result()
           ^^^^^^^^^^^^^^^
  File "<@beartype(sotopia.server.run_async_server) at 0x7fc7c76bb740>", line 260, in run_async_server
  File "/home/yufansong/miniconda3/envs/bridge/lib/python3.11/site-packages/sotopia/server.py", line 294, in run_async_server
    episode_futures = [
                      ^
  File "/home/yufansong/miniconda3/envs/bridge/lib/python3.11/site-packages/sotopia/server.py", line 294, in <listcomp>
    episode_futures = [
                      ^
  File "/home/yufansong/miniconda3/envs/bridge/lib/python3.11/site-packages/sotopia/samplers/uniform_sampler.py", line 56, in sample
    env_profile = random.choice(self.env_candidates)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/yufansong/miniconda3/envs/bridge/lib/python3.11/random.py", line 373, in choice
    raise IndexError('Cannot choose from an empty sequence')
IndexError: Cannot choose from an empty sequence

Closes #

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• [ ] My pull request adheres to the code style of this project
• [ ] My code requires changes to the documentation
• [ ] I have updated the documentation as required
• [ ] All the tests have passed
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ℹ Additional Information

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 66.66667% with 4 lines in your changes missing coverage. Please review.

Project coverage is 71.49%. Comparing base (2a51167) to head (aec1d2b). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
sotopia/samplers/uniform_sampler.py	57.14%	3 Missing :warning:
sotopia/samplers/constraint_based_sampler.py	80.00%	1 Missing :warning:

@@            Coverage Diff             @@
##             main     #211      +/-   ##
==========================================
- Coverage   71.53%   71.49%   -0.04%     
==========================================
  Files          55       55              
  Lines        2863     2863              
==========================================
- Hits         2048     2047       -1     
- Misses        815      816       +1     

Files with missing lines	Coverage Δ
sotopia/samplers/constraint_based_sampler.py	90.90% <80.00%> (ø)
sotopia/samplers/uniform_sampler.py	84.84% <57.14%> (ø)

... and 1 file with indirect coverage changes