feat: make BaseError#walk tolerant to an undefined cause (#2954)

* Make BaseError#walk tolerant to an undefined cause

* Create khaki-queens-explain.md

---------

Co-authored-by: jxom <j@wevm.dev>

.changeset/khaki-queens-explain.md

@@ -0,0 +1,5 @@
+---
+"viem": patch
+---
+
+Make `BaseError#walk` tolerant to an `undefined` cause.

src/errors/base.test.ts

@@ -179,6 +179,15 @@ test('walk: predicate fn (no match)', () => {
   expect(err.walk((err) => err instanceof FooError)).toBeNull()
 })
 
+test('walk: undefined cause', () => {
+  const withCauseUndefined = new Error('Cuase undefined', { cause: undefined })
+
+  const err = new BaseError('test1', {
+    cause: withCauseUndefined,
+  })
+  expect(err.walk()).toBe(withCauseUndefined)
+})
+
 test('setErrorConfig', () => {
   class FooError extends BaseError {
     constructor() {

src/errors/base.ts

@@ -87,7 +87,7 @@ function walk(
   fn?: ((err: unknown) => boolean) | undefined,
 ): unknown {
   if (fn?.(err)) return err
-  if (err && typeof err === 'object' && 'cause' in err)
+  if (err && typeof err === 'object' && 'cause' in err && err.cause !== undefined)
     return walk(err.cause, fn)
   return fn ? null : err
 }