Nullable array models generate failing code

[kgutwin]

Describe the bug
When an array is marked as nullable (in OpenAPI 3.0 or 3.1) the generated code fails type checking with the message:

error: Incompatible types in assignment (expression has type "tuple[None, bytes, str]", variable has type "list[float] | Unset | None")  [assignment]

From the end-to-end test suite, making some_array nullable (part of Body_upload_file_tests_upload_post) results in this change:

@@ -165,10 +172,17 @@ class BodyUploadFileTestsUploadPost:
             else (None, str(self.some_number).encode(), "text/plain")
         )
 
-        some_array: Union[Unset, Tuple[None, bytes, str]] = UNSET
-        if not isinstance(self.some_array, Unset):
-            _temp_some_array = self.some_array
-            some_array = (None, json.dumps(_temp_some_array).encode(), "application/json")
+        some_array: Union[List[float], None, Unset]
+        if isinstance(self.some_array, Unset):
+            some_array = UNSET
+        elif isinstance(self.some_array, list):
+            some_array = UNSET
+            if not isinstance(self.some_array, Unset):
+                _temp_some_array = self.some_array
+                some_array = (None, json.dumps(_temp_some_array).encode(), "application/json")
+
+        else:
+            some_array = self.some_array
 
         some_optional_object: Union[Unset, Tuple[None, bytes, str]] = UNSET

OpenAPI Spec File
The following patch applied the end-to-end test suite reproduces the problem:

diff --git a/end_to_end_tests/baseline_openapi_3.0.json b/end_to_end_tests/baseline_openapi_3.0.json
index d21d1d5..25adeaa 100644
--- a/end_to_end_tests/baseline_openapi_3.0.json
+++ b/end_to_end_tests/baseline_openapi_3.0.json
@@ -1778,6 +1778,7 @@
           },
           "some_array": {
             "title": "Some Array",
+            "nullable": true,
             "type": "array",
             "items": {
               "type": "number"
diff --git a/end_to_end_tests/baseline_openapi_3.1.yaml b/end_to_end_tests/baseline_openapi_3.1.yaml
index 03270af..4e33e68 100644
--- a/end_to_end_tests/baseline_openapi_3.1.yaml
+++ b/end_to_end_tests/baseline_openapi_3.1.yaml
@@ -1794,7 +1794,7 @@ info:
         },
         "some_array": {
           "title": "Some Array",
-          "type": "array",
+          "type": [ "array", "null" ],
           "items": {
             "type": "number"
           }

Desktop (please complete the following information):

• openapi-python-client version 0.17.0

[kgutwin]

If the item type is an object rather than a simple type, another type checking error is found:

error: "Unset" has no attribute "append"  [attr-defined]

To reproduce in end-to-end tests:

diff --git a/end_to_end_tests/baseline_openapi_3.0.json b/end_to_end_tests/baseline_openapi_3.0.json
index d21d1d5..f9a33e5 100644
--- a/end_to_end_tests/baseline_openapi_3.0.json
+++ b/end_to_end_tests/baseline_openapi_3.0.json
@@ -1778,9 +1778,10 @@
           },
           "some_array": {
             "title": "Some Array",
+            "nullable": true,
             "type": "array",
             "items": {
-              "type": "number"
+              "$ref": "#/components/schemas/AFormData"
             }
           },
           "some_object": {
diff --git a/end_to_end_tests/baseline_openapi_3.1.yaml b/end_to_end_tests/baseline_openapi_3.1.yaml
index 03270af..78fa7fb 100644
--- a/end_to_end_tests/baseline_openapi_3.1.yaml
+++ b/end_to_end_tests/baseline_openapi_3.1.yaml
@@ -1794,9 +1794,9 @@ info:
         },
         "some_array": {
           "title": "Some Array",
-          "type": "array",
+          "type": [ "array", "null" ],
           "items": {
-            "type": "number"
+            "$ref": "#/components/schemas/AFormData"
           }
         },
         "some_object": {

Affected resulting generated code (end_to_end_tests/golden-record/my_test_api_client/models/body_upload_file_tests_upload_post.py):

@@ -265,7 +287,27 @@ class BodyUploadFileTestsUploadPost:
 
         some_number = d.pop("some_number", UNSET)
 
-        some_array = cast(List[float], d.pop("some_array", UNSET))
+        def _parse_some_array(data: object) -> Union[List["AFormData"], None, Unset]:
+            if data is None:
+                return data
+            if isinstance(data, Unset):
+                return data
+            try:
+                if not isinstance(data, list):
+                    raise TypeError()
+                some_array_type_0 = UNSET
+                _some_array_type_0 = data
+                for some_array_type_0_item_data in _some_array_type_0 or []:
+                    some_array_type_0_item = AFormData.from_dict(some_array_type_0_item_data)
+
+                    some_array_type_0.append(some_array_type_0_item)
+
+                return some_array_type_0
+            except:  # noqa: E722
+                pass
+            return cast(Union[List["AFormData"], None, Unset], data)
+
+        some_array = _parse_some_array(d.pop("some_array", UNSET))
 
         _some_optional_object = d.pop("some_optional_object", UNSET)
         some_optional_object: Union[Unset, BodyUploadFileTestsUploadPostSomeOptionalObject]