diff --git a/rivetkit-typescript/packages/rivetkit/src/actor/protocol/old.ts b/rivetkit-typescript/packages/rivetkit/src/actor/protocol/old.ts
index 0854a8d2e5..c830cd86f3 100644
--- a/rivetkit-typescript/packages/rivetkit/src/actor/protocol/old.ts
+++ b/rivetkit-typescript/packages/rivetkit/src/actor/protocol/old.ts
@@ -299,20 +299,29 @@ export async function processMessage<
 				errorData,
 				TO_CLIENT_VERSIONED,
 				ToClientSchema,
-				// JSON: metadata is the raw value
-				(value): ToClientJson => ({
-					body: {
-						tag: "Error" as const,
-						val: {
-							group: value.group,
-							code: value.code,
-							message: value.message,
-							metadata: value.metadata ?? null,
-							actionId: value.actionId ?? null,
+				// JSON: metadata is the raw value (keep as undefined if not present)
+				(value): ToClientJson => {
+					const val: any = {
+						group: value.group,
+						code: value.code,
+						message: value.message,
+						actionId:
+							value.actionId !== undefined
+								? value.actionId
+								: null,
+					};
+					if (value.metadata !== undefined) {
+						val.metadata = value.metadata;
+					}
+					return {
+						body: {
+							tag: "Error" as const,
+							val,
 						},
-					},
-				}),
+					};
+				},
 				// BARE/CBOR: metadata needs to be CBOR-encoded to ArrayBuffer
+				// Note: protocol.Error expects `| null` for optional fields (BARE protocol)
 				(value): protocol.ToClient => ({
 					body: {
 						tag: "Error" as const,
@@ -325,7 +334,10 @@ export async function processMessage<
 										cbor.encode(value.metadata),
 									)
 								: null,
-							actionId: value.actionId ?? null,
+							actionId:
+								value.actionId !== undefined
+									? value.actionId
+									: null,
 						},
 					},
 				}),
diff --git a/rivetkit-typescript/packages/rivetkit/src/client/utils.ts b/rivetkit-typescript/packages/rivetkit/src/client/utils.ts
index 2aa66ac858..3c4506a6b8 100644
--- a/rivetkit-typescript/packages/rivetkit/src/client/utils.ts
+++ b/rivetkit-typescript/packages/rivetkit/src/client/utils.ts
@@ -157,7 +157,7 @@ export async function sendHttpRequest<
 					message: bare.message,
 					metadata: bare.metadata
 						? cbor.decode(new Uint8Array(bare.metadata))
-						: null,
+						: undefined,
 				}),
 			);
 		} catch (error) {
diff --git a/rivetkit-typescript/packages/rivetkit/src/common/router.ts b/rivetkit-typescript/packages/rivetkit/src/common/router.ts
index f86e68437c..530f26ec73 100644
--- a/rivetkit-typescript/packages/rivetkit/src/common/router.ts
+++ b/rivetkit-typescript/packages/rivetkit/src/common/router.ts
@@ -82,7 +82,7 @@ export function handleRouteError(error: unknown, c: HonoContext) {
 			group: value.group,
 			code: value.code,
 			message: value.message,
-			metadata: value.metadata ?? null,
+			metadata: value.metadata,
 		}),
 		// BARE/CBOR: metadata needs to be CBOR-encoded to ArrayBuffer
 		(value): protocol.HttpResponseError => ({
diff --git a/rivetkit-typescript/packages/rivetkit/src/schemas/client-protocol-zod/mod.ts b/rivetkit-typescript/packages/rivetkit/src/schemas/client-protocol-zod/mod.ts
index ca70a30023..8460f713ac 100644
--- a/rivetkit-typescript/packages/rivetkit/src/schemas/client-protocol-zod/mod.ts
+++ b/rivetkit-typescript/packages/rivetkit/src/schemas/client-protocol-zod/mod.ts
@@ -15,7 +15,7 @@ export const ErrorSchema = z.object({
 	group: z.string(),
 	code: z.string(),
 	message: z.string(),
-	metadata: z.unknown().nullable(),
+	metadata: z.unknown().optional(),
 	actionId: OptionalUintSchema,
 });
 export type Error = z.infer<typeof ErrorSchema>;
@@ -89,7 +89,7 @@ export const HttpResponseErrorSchema = z.object({
 	group: z.string(),
 	code: z.string(),
 	message: z.string(),
-	metadata: z.unknown().nullable(),
+	metadata: z.unknown().optional(),
 });
 export type HttpResponseError = z.infer<typeof HttpResponseErrorSchema>;