minor fix for state only envs

env.py

@@ -428,8 +428,8 @@ def _create_isaaclab_env(config: dict, n_envs: int) -> dict[str, dict[int, gym.v
         logging.info(f"Set render_mode={render_mode} on underlying IsaacLab env")
 
     # Validate config
-    state_keys = tuple(k.strip() for k in config.get("state_keys", "").split(",") if k.strip())
-    camera_keys = tuple(k.strip() for k in config.get("camera_keys", "").split(",") if k.strip())
+    state_keys = tuple(k.strip() for k in (config.get("state_keys") or "").split(",") if k.strip())
+    camera_keys = tuple(k.strip() for k in (config.get("camera_keys") or "").split(",") if k.strip())
     validate_config(
         raw_env, state_keys, camera_keys,
         config.get("state_dim", 54),