Fix default handling for ZCLCommandButtonMetadata

tests/test_quirks_v2.py

@@ -626,6 +626,10 @@ async def test_quirks_v2_command_button(device_mock):
                 "on_off_control_foo": OnOff.OnOffControl.Accept_Only_When_On
             },
         )
+        .command_button(
+            OnOff.ServerCommandDefs.on_with_timed_off.name,
+            OnOff.cluster_id,
+        )
         .add_to_registry()
     )
 
@@ -634,7 +638,6 @@ async def test_quirks_v2_command_button(device_mock):
 
     assert quirked_device.endpoints[1].in_clusters.get(OnOff.cluster_id) is not None
 
-    # pylint: disable=line-too-long
     button: EntityMetadata = quirked_device.exposes_metadata[
         (1, OnOff.cluster_id, ClusterType.Server)
     ][0]
@@ -655,6 +658,13 @@ async def test_quirks_v2_command_button(device_mock):
     )
     assert button != quirked_device
 
+    button = quirked_device.exposes_metadata[(1, OnOff.cluster_id, ClusterType.Server)][
+        2
+    ]
+
+    assert button.kwargs == {}
+    assert button.args == ()
+
 
 async def test_quirks_v2_also_applies_to(device_mock):
     """Test adding the same quirk for multiple manufacturers and models."""

zigpy/quirks/v2/__init__.py

@@ -784,8 +784,8 @@ def command_button(
                 initially_disabled=initially_disabled,
                 translation_key=translation_key,
                 command_name=command_name,
-                args=command_args,
-                kwargs=command_kwargs,
+                args=command_args if command_args is not None else (),
+                kwargs=command_kwargs if command_kwargs is not None else frozendict(),
             )
         )
         return self