📝 Update Request Body's tutorial002 to deal with tax=0 case (#13230)

Co-authored-by: svlandeg <svlandeg@github.com>

docs_src/body/tutorial002.py

@@ -17,7 +17,7 @@ app = FastAPI()
 @app.post("/items/")
 async def create_item(item: Item):
     item_dict = item.dict()
-    if item.tax:
+    if item.tax is not None:
         price_with_tax = item.price + item.tax
         item_dict.update({"price_with_tax": price_with_tax})
     return item_dict

docs_src/body/tutorial002_py310.py

@@ -15,7 +15,7 @@ app = FastAPI()
 @app.post("/items/")
 async def create_item(item: Item):
     item_dict = item.dict()
-    if item.tax:
+    if item.tax is not None:
         price_with_tax = item.price + item.tax
         item_dict.update({"price_with_tax": price_with_tax})
     return item_dict