Fix optional field doesn't include None (#1411)

* Fix optional field doesn't include `None`

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

datamodel_code_generator/model/template/pydantic_v2/BaseModel.jinja2

@@ -24,7 +24,7 @@ class {{ class_name }}({{ base_class }}):{% if comment is defined %}  # {{ comme
     {%- else %}
     {{ field.name }}: {{ field.type_hint }}
     {%- endif %}
-    {%- if not (field.required or (field.represented_default == 'None' and field.strip_default_none))
+    {%- if not field.required or field.data_type.is_optional or field.nullable
             %} = {{ field.represented_default }}
     {%- endif -%}
     {%- endif %}

tests/data/expected/main/main_null_and_array_v2/output.py

@@ -0,0 +1,17 @@
+# generated by datamodel-codegen:
+#   filename:  null_and_array.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from typing import Any, List, Optional
+
+from pydantic import BaseModel
+
+
+class MyObjItem(BaseModel):
+    items: Optional[List[Any]] = None
+
+
+class Model(BaseModel):
+    my_obj: List[MyObjItem]

tests/test_main.py

@@ -432,8 +432,21 @@ def test_main_json_array_include_null():
         )
 
 
+@pytest.mark.parametrize(
+    'output_model,expected_output',
+    [
+        (
+            'pydantic.BaseModel',
+            'main_null_and_array',
+        ),
+        (
+            'pydantic_v2.BaseModel',
+            'main_null_and_array_v2',
+        ),
+    ],
+)
 @freeze_time('2019-07-26')
-def test_main_null_and_array():
+def test_main_null_and_array(output_model, expected_output):
     with TemporaryDirectory() as output_dir:
         output_file: Path = Path(output_dir) / 'output.py'
         return_code: Exit = main(
@@ -444,12 +457,14 @@ def test_main_null_and_array():
                 str(output_file),
                 '--input-file-type',
                 'jsonschema',
+                '--output-model',
+                output_model,
             ]
         )
         assert return_code == Exit.OK
         assert (
             output_file.read_text()
-            == (EXPECTED_MAIN_PATH / 'main_null_and_array' / 'output.py').read_text()
+            == (EXPECTED_MAIN_PATH / expected_output / 'output.py').read_text()
         )