fix: set default to None for optional fields

- Fix in Pydantic Python Generator for optional values.
- default=None should be added in `Field()` if the property is optional.

Signed-off-by: Harshil Jani <harshiljani2002@gmail.com>

src/generators/python/presets/Pydantic.ts

@@ -18,14 +18,20 @@ const PYTHON_PYDANTIC_CLASS_PRESET: ClassPresetType<PythonOptions> = {
     );
   },
   property(params) {
-    const type = params.property.required
-      ? params.property.property.type
-      : `Optional[${params.property.property.type}]`;
-    const alias = params.property.property.originalInput['description']
-      ? `alias='''${params.property.property.originalInput['description']}'''`
-      : '';
-
-    return `${params.property.propertyName}: ${type} = Field(${alias})`;
+    const { propertyName, required, property } = params.property;
+    const type = required ? property.type : `Optional[${property.type}]`;
+    const description = property.originalInput['description'];
+    const alias = description ? `alias='''${description}'''` : '';
+    const defaultValue = required ? '' : 'default=None';
+    return (
+      alias && defaultValue
+        ? `${propertyName}: ${type} = Field(${alias}, ${defaultValue})`
+        : alias
+          ? `${propertyName}: ${type} = Field(${alias})`
+          : defaultValue
+            ? `${propertyName}: ${type} = Field(${defaultValue})`
+            : ''
+    );
   },
   ctor: () => '',
   getter: () => '',