Fix type error

src/api/openrouter.ts

@@ -259,8 +259,7 @@ export class OpenRouterHandler implements ApiHandler {
 						role: "assistant",
 						content: textContent,
 						tool_calls: toolCalls.length > 0 ? toolCalls : undefined,
-						// @ts-ignore-next-line
-						refusal: undefined,
+						refusal: null,
 					},
 					finish_reason: toolCalls.length > 0 ? "tool_calls" : "stop",
 					index: 0,