[CLI] fix cluster creation CLI requiring instance-type selection (#14056)

fix cluster creation CLI requiring instace-type selection

we've marked `instance_types` as `required=False`, but the CLI calls `split` on the value.
So if nothing is provided, we'll actually receive a runtime error, effectively rendering the flag as required.

Co-authored-by: thomas chaton <thomas@grid.ai>

Author: nicolai86

src/lightning_app/cli/lightning_cli_create.py

@@ -79,7 +79,7 @@ def create_cluster(
         region=region,
         role_arn=role_arn,
         external_id=external_id,
-        instance_types=instance_types.split(","),
+        instance_types=instance_types.split(",") if instance_types is not None else None,
         edit_before_creation=edit_before_creation,
         cost_savings=cost_savings,
         wait=wait,

tests/tests_app/cli/test_cli.py

@@ -70,7 +70,15 @@ def test_main_lightning_cli_help():
 
 @mock.patch("lightning_cloud.login.Auth.authenticate", MagicMock())
 @mock.patch("lightning_app.cli.cmd_clusters.AWSClusterManager.create")
-def test_create_cluster(create: mock.MagicMock):
+@pytest.mark.parametrize(
+    "instance_types,expected_instance_types",
+    [
+        (["--instance-types", "t3.xlarge"], ["t3.xlarge"]),
+        (["--instance-types", "t3.xlarge,t3.2xlarge"], ["t3.xlarge", "t3.2xlarge"]),
+        ([], None),
+    ],
+)
+def test_create_cluster(create_command: mock.MagicMock, instance_types, expected_instance_types):
     runner = CliRunner()
     runner.invoke(
         create_cluster,
@@ -82,17 +90,16 @@ def test_create_cluster(create: mock.MagicMock):
             "dummy",
             "--role-arn",
             "arn:aws:iam::1234567890:role/lai-byoc",
-            "--instance-types",
-            "t2.small",
-        ],
+        ]
+        + instance_types,
     )
 
-    create.assert_called_once_with(
+    create_command.assert_called_once_with(
         cluster_name="test-7",
         region="us-east-1",
         role_arn="arn:aws:iam::1234567890:role/lai-byoc",
         external_id="dummy",
-        instance_types=["t2.small"],
+        instance_types=expected_instance_types,
         edit_before_creation=False,
         cost_savings=False,
         wait=False,