chore(python): unbreak optional fields on Python 3.7

The error was: TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

See https://stackoverflow.com/questions/76712720/typeerror-unsupported-operand-types-for-type-and-nonetype

Correction for 67a664a commit.

Part of #16
Relate to #13

examples/python/fastapi/postgres/routes.py

@@ -5,15 +5,17 @@
 
 from pydantic import BaseModel
 
+from typing import Optional
+
 from db import db_connection
 
 router = APIRouter()
 
 class CreateCategoryDto(BaseModel):
-    name: str | None = None
-    name_ru: str | None = None
-    slug: str | None = None
-    user_id: int | None = None
+    name: Optional[str] = None
+    name_ru: Optional[str] = None
+    slug: Optional[str] = None
+    user_id: Optional[int] = None
 
 
 @router.get('/v1/categories/count')

src/templates/routes.py.ejs

@@ -7,6 +7,9 @@ from fastapi import APIRouter, Depends, HTTPException, status
 <%# LATER: add only when POST/PUT endpoints are present -%>
 from pydantic import BaseModel
 
+<%# LATER: add only when POST/PUT endpoints are present -%>
+from typing import Optional
+
 from db import db_connection
 
 router = APIRouter()
@@ -114,7 +117,7 @@ function query2dto(parser, method) {
 function dto2model(dto) {
 	let result = `class ${dto.name}(BaseModel):\n`;
 	dto.props.forEach(prop => {
-		result += `    ${prop.name}: ${prop.type} | None = None\n`
+		result += `    ${prop.name}: Optional[${prop.type}] = None\n`
 	});
 	return result;
 }