request json is nullable

starlette/requests.py

@@ -236,10 +236,10 @@ async def body(self) -> bytes:
             self._body = b"".join(chunks)
         return self._body
 
-    async def json(self) -> typing.Any:
+    async def json(self, nullable: bool = False) -> typing.Any:
         if not hasattr(self, "_json"):
             body = await self.body()
-            self._json = json.loads(body)
+            self._json = {} if (body == b'' and nullable) else json.loads(body)
         return self._json
 
     async def form(self) -> FormData:

tests/test_requests.py

@@ -166,10 +166,22 @@ async def app(scope, receive, send):
         await response(scope, receive, send)
 
     client = test_client_factory(app)
-    response = client.post("/", json={"a": "123"})
+    response = client.post("/", json={'a': '123'})
     assert response.json() == {"json": {"a": "123"}}
 
 
+def test_request_json_null(test_client_factory):
+    async def app(scope, receive, send):
+        request = Request(scope, receive)
+        data = await request.json(nullable=True)
+        response = JSONResponse({"json": data})
+        await response(scope, receive, send)
+
+    client = test_client_factory(app)
+    response = client.post("/")
+    assert response.json() == {"json": {}}
+
+
 def test_request_scope_interface():
     """
     A Request can be instantiated with a scope, and presents a `Mapping`