diff --git a/docs/walkthrough.md b/docs/walkthrough.md
index 33aab88..9d77764 100644
--- a/docs/walkthrough.md
+++ b/docs/walkthrough.md
@@ -189,8 +189,9 @@ and a switch over them says what is wrong:
 
 <!-- sample: samples/Bookings/BookingApi.cs -->
 ```csharp
-static string? CheckStay(DateRange stay) => stay switch
+static string? CheckStay(DateRange? stay) => stay switch
 {
+    null => "Give the stay.",
     DateRange.Finite { Length: > 30 } => "A stay is at most 30 nights.",
     DateRange.Finite => null,
     DateRange.EmptyRange => "The stay has no nights.",
@@ -211,6 +212,9 @@ JSON body, the converter throws. Either way the response is a 400 with an empty
 
 Good to know:
 
+- **A JSON `null` reaches the handler.** System.Text.Json doesn't check nullable annotations unless
+  you turn on `RespectNullableAnnotations`. So `"stay":null`, or a body with no `stay`, binds as
+  `null` although `Stay` isn't nullable, and the `null` arm turns it into a 400.
 - **The discard arm is there for the compiler.** The five shapes are the only ones that can exist,
   but C# can't prove it. [Pattern matching](ranges.md#pattern-matching) explains why the discard
   should throw.
diff --git a/samples/Bookings/BookingApi.cs b/samples/Bookings/BookingApi.cs
index 33f48a1..bbb2dae 100644
--- a/samples/Bookings/BookingApi.cs
+++ b/samples/Bookings/BookingApi.cs
@@ -108,8 +108,9 @@ static async Task<IResult> GetAvailability(int id, DateRange window, BookingCont
         return TypedResults.Ok(new Availability(id, window, booked, free));
     }
 
-    static string? CheckStay(DateRange stay) => stay switch
+    static string? CheckStay(DateRange? stay) => stay switch
     {
+        null => "Give the stay.",
         DateRange.Finite { Length: > 30 } => "A stay is at most 30 nights.",
         DateRange.Finite => null,
         DateRange.EmptyRange => "The stay has no nights.",
diff --git a/test/CodoMetis.ValueRanges.EFCore.PostgreSQL.IntegrationTests/WalkthroughSampleTests.cs b/test/CodoMetis.ValueRanges.EFCore.PostgreSQL.IntegrationTests/WalkthroughSampleTests.cs
index 367838a..7259dbe 100644
--- a/test/CodoMetis.ValueRanges.EFCore.PostgreSQL.IntegrationTests/WalkthroughSampleTests.cs
+++ b/test/CodoMetis.ValueRanges.EFCore.PostgreSQL.IntegrationTests/WalkthroughSampleTests.cs
@@ -77,7 +77,7 @@ await sample.Expect(HttpStatusCode.Created,
     }
 
     [TestMethod]
-    public async Task Validation_RejectsAnOpenStay_AStayOutOfSeason_AndALiteralThatDoesNotParse()
+    public async Task Validation_RejectsANullStay_AnOpenStay_AStayOutOfSeason_AndALiteralThatDoesNotParse()
     {
         await using var sample = await SampleHost.StartAsync();
 
@@ -91,6 +91,11 @@ await sample.Expect(HttpStatusCode.BadRequest, Problem + """{"stay":["A stay is
             sample.Post("""{"roomId":1,"guest":"Linus","stay":"[2026-08-01,2026-09-01)"}"""));
         await sample.Expect(HttpStatusCode.Created, null,
             sample.Post("""{"roomId":1,"guest":"Linus","stay":"[2026-08-01,2026-08-31)"}"""));
+        // System.Text.Json binds a JSON null, or no stay at all, as null whatever the annotation (#465).
+        await sample.Expect(HttpStatusCode.BadRequest, Problem + """{"stay":["Give the stay."]}}""",
+            sample.Post("""{"roomId":1,"guest":"Linus","stay":null}"""));
+        await sample.Expect(HttpStatusCode.BadRequest, Problem + """{"stay":["Give the stay."]}}""",
+            sample.Post("""{"roomId":1,"guest":"Linus"}"""));
         await sample.Expect(HttpStatusCode.BadRequest, Problem + """{"guest":["Name the guest."]}}""",
             sample.Post("""{"roomId":1,"stay":"[2026-09-01,2026-09-03)"}"""));
         await sample.Expect(HttpStatusCode.BadRequest, Problem + """{"stay":["Garden takes bookings for [2026-05-01,2026-09-30] only."]}}""",