fix: "undefined" string in characteristic error warnings

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bwp91

CHANGELOG.md

@@ -21,6 +21,7 @@ All notable changes to `@homebridge/hap-nodejs` will be documented in this file.
 - fix: category defaulting to string instead of enum
 - fix: missing error argument in pairing debug logs
 - fix: use constant-time comparison for pincode checks
+- fix: `"undefined"` string in characteristic error warnings
 
 ## v2.1.2 (2026-03-29)
 

src/lib/Characteristic.ts

@@ -2118,7 +2118,7 @@ export class Characteristic extends EventEmitter {
     try {
       value = this.validateUserInput(value)!;
     } catch (error) {
-      this.characteristicWarning(error?.message + "", CharacteristicWarningType.ERROR_MESSAGE, error?.stack);
+      this.characteristicWarning(error?.message || "Unknown error", CharacteristicWarningType.ERROR_MESSAGE, error?.stack);
       if (callback) {
         callback(error);
       }
@@ -2204,7 +2204,7 @@ export class Characteristic extends EventEmitter {
     try {
       value = this.validateUserInput(value);
     } catch (error) {
-      this.characteristicWarning(error?.message + "", CharacteristicWarningType.ERROR_MESSAGE, error?.stack);
+      this.characteristicWarning(error?.message || "Unknown error", CharacteristicWarningType.ERROR_MESSAGE, error?.stack);
       if (callback) {
         callback();
       }