From 9a48040c562d28c3e8a1e0057df886b7d9f053ab Mon Sep 17 00:00:00 2001
From: LeCarbonator <18158911+LeCarbonator@users.noreply.github.com>
Date: Mon, 22 Dec 2025 09:18:21 +0100
Subject: [PATCH 1/3] chore(form-core): use conditional chains again

---
 packages/form-core/src/FormApi.ts | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/packages/form-core/src/FormApi.ts b/packages/form-core/src/FormApi.ts
index 5b1ec5e17..ff52bbe74 100644
--- a/packages/form-core/src/FormApi.ts
+++ b/packages/form-core/src/FormApi.ts
@@ -1696,8 +1696,11 @@ export class FormApi<
             determineFormLevelErrorSourceAndValue({
               newFormValidatorError,
               isPreviousErrorFromFormValidator:
-                currentErrorMapSource[errorMapKey] === 'form',
-              previousErrorValue: currentErrorMap[errorMapKey],
+                // These conditional checks are required, otherwise we get runtime errors.
+                // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+                currentErrorMapSource?.[errorMapKey] === 'form',
+              // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+              previousErrorValue: currentErrorMap?.[errorMapKey],
             })
 
           if (newSource === 'form') {
@@ -1707,7 +1710,9 @@ export class FormApi<
             }
           }
 
-          if (currentErrorMap[errorMapKey] !== newErrorValue) {
+          // This conditional check is required, otherwise we get runtime errors.
+          // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+          if (currentErrorMap?.[errorMapKey] !== newErrorValue) {
             this.setFieldMeta(field, (prev = defaultFieldMeta) => ({
               ...prev,
               errorMap: {

From 7f77f32ad4bc4fe6ad4c8a39748d5aaab89e3c03 Mon Sep 17 00:00:00 2001
From: LeCarbonator <18158911+LeCarbonator@users.noreply.github.com>
Date: Mon, 22 Dec 2025 09:20:33 +0100
Subject: [PATCH 2/3] Fix runtime errors in form-core validation

Prevent runtime errors that occur during form validation in the form-core package.
---
 .changeset/dull-bees-draw.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/dull-bees-draw.md

diff --git a/.changeset/dull-bees-draw.md b/.changeset/dull-bees-draw.md
new file mode 100644
index 000000000..57c06e9ee
--- /dev/null
+++ b/.changeset/dull-bees-draw.md
@@ -0,0 +1,5 @@
+---
+"@tanstack/form-core": patch
+---
+
+fix(form-core): Prevent runtime errors during validation

From f68391ca10a176c6787e7abe334eb625779e01bb Mon Sep 17 00:00:00 2001
From: "autofix-ci[bot]" <114827586+autofix-ci[bot]@users.noreply.github.com>
Date: Mon, 22 Dec 2025 08:21:20 +0000
Subject: [PATCH 3/3] ci: apply automated fixes and generate docs

---
 .changeset/dull-bees-draw.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.changeset/dull-bees-draw.md b/.changeset/dull-bees-draw.md
index 57c06e9ee..8a09ca242 100644
--- a/.changeset/dull-bees-draw.md
+++ b/.changeset/dull-bees-draw.md
@@ -1,5 +1,5 @@
 ---
-"@tanstack/form-core": patch
+'@tanstack/form-core': patch
 ---
 
 fix(form-core): Prevent runtime errors during validation