update

ts/forwarding/handlers/base-handler.ts

@@ -104,13 +104,15 @@ export abstract class ForwardingHandler extends plugins.EventEmitter implements
     
     // Apply custom headers with variable substitution
     for (const [key, value] of Object.entries(customHeaders)) {
+      if (typeof value !== 'string') continue;
+
       let processedValue = value;
-      
+
       // Replace variables in the header value
       for (const [varName, varValue] of Object.entries(variables)) {
         processedValue = processedValue.replace(`{${varName}}`, varValue);
       }
-      
+
       result[key] = processedValue;
     }