【优化】AI 角色分类，处理 role 空情况

yudao-module-ai/yudao-module-ai-biz/src/main/java/cn/iocoder/yudao/module/ai/service/model/AiChatRoleServiceImpl.java

@@ -137,7 +137,7 @@ public class AiChatRoleServiceImpl implements AiChatRoleService {
     @Override
     public List<String> getChatRoleCategoryList() {
         List<AiChatRoleDO> list = chatRoleMapper.selectListGroupByCategory(CommonStatusEnum.ENABLE.getStatus());
-        return convertList(list, AiChatRoleDO::getCategory, role -> StrUtil.isNotBlank(role.getCategory()));
+        return convertList(list, AiChatRoleDO::getCategory, role -> role != null && StrUtil.isNotBlank(role.getCategory()));
     }
 
 }