From aadc24d47d81c4d672c65257d13f30f598a9064b Mon Sep 17 00:00:00 2001
From: Mark Probst <mark.probst@gmail.com>
Date: Mon, 6 Jul 2026 16:18:23 -0400
Subject: [PATCH 1/2] Dart: null-guard nullable date fields in toJson

For a nullable "date" transformed-string field, the Dart renderer's
toJson emitted a template string over `x!.year` / `x!.month` / `x!.day`
with no null check, so serializing an instance whose date field is null
threw "Null check operator used on a null value" at runtime.  Nullable
date-time fields were already handled correctly with
`?.toIso8601String()`.

Emit `x == null ? null : "${x!...}"` in the null-safe nullable branch,
mirroring the null guards used in fromJson.

Adds test/inputs/json/priority/bug2590.json, a fixture input with a
nullable yyyy-mm-dd date field, so the dart fixture round-trips it in
CI.

Fixes #2590

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 .../src/language/Dart/DartRenderer.ts              |  3 ++-
 test/inputs/json/priority/bug2590.json             | 14 ++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)
 create mode 100644 test/inputs/json/priority/bug2590.json

diff --git a/packages/quicktype-core/src/language/Dart/DartRenderer.ts b/packages/quicktype-core/src/language/Dart/DartRenderer.ts
index f5220d2505..3c24da88df 100644
--- a/packages/quicktype-core/src/language/Dart/DartRenderer.ts
+++ b/packages/quicktype-core/src/language/Dart/DartRenderer.ts
@@ -603,7 +603,8 @@ export class DartRenderer extends ConvenienceRenderer {
                             (transformedStringType.isNullable || isNullable)
                         ) {
                             return [
-                                '"${',
+                                dynamic,
+                                ' == null ? null : "${',
                                 dynamic,
                                 "!.year.toString().padLeft(4, '0')",
                                 "}-${",
diff --git a/test/inputs/json/priority/bug2590.json b/test/inputs/json/priority/bug2590.json
new file mode 100644
index 0000000000..60e067955a
--- /dev/null
+++ b/test/inputs/json/priority/bug2590.json
@@ -0,0 +1,14 @@
+{
+    "invoices": [
+        {
+            "name": "invoice-1",
+            "dueDate": "2023-01-15",
+            "createdAt": "2023-01-15T10:30:00Z"
+        },
+        {
+            "name": "invoice-2",
+            "dueDate": null,
+            "createdAt": null
+        }
+    ]
+}

From 37d0f9066190833b53dbeeaeb4bcb9e3dc671181 Mon Sep 17 00:00:00 2001
From: Mark Probst <mark.probst@gmail.com>
Date: Mon, 6 Jul 2026 16:47:49 -0400
Subject: [PATCH 2/2] Skip nullable date-time fixture for TypeScript-Zod

---
 test/languages.ts | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/test/languages.ts b/test/languages.ts
index a31f78b6f5..c9cdccdab2 100644
--- a/test/languages.ts
+++ b/test/languages.ts
@@ -1563,6 +1563,9 @@ export const TypeScriptZodLanguage: Language = {
         // Does not handle top level array
         "bug863.json",
 
+        // z.coerce.date() coerces null to the Unix epoch: #2880
+        "bug2590.json",
+
         "no-classes.json",
         "00c36.json",
         "10be4.json",