Fix default config dicts (#329)

* Fix default config dicts

* style

Author: sgugger

src/accelerate/commands/config/config_args.py

@@ -139,6 +139,13 @@ class ClusterConfig(BaseConfig):
     # args for fsdp
     fsdp_config: dict = None
 
+    def __post_init__(self):
+        if self.deepspeed_config is None:
+            self.deepspeed_config = {}
+        if self.fsdp_config is None:
+            self.fsdp_config = {}
+        return super().__post_init__()
+
 
 @dataclass
 class SageMakerConfig(BaseConfig):