Continuous integration Gitlab CI正在清理基于文件的变量错误：退出状态1

我正在使用fastlane和Gitlab CI构建iOS项目。GItlab runner作为shell运行。这是yml文件

before_script:
  - export LC_ALL=en_US.UTF-8
  - export LANG=en_US.UTF-8
  - export BUILD_TIME=$(date '+%Y-%m-%d %H:%M:%S')
  - echo $branch
  
stages:
  - build
  
build_job:
  stage: build
  tags:
    - ClaimIt2020
    - iOS
  only:
    variables:
      - $branch
  script:
    - bundle install
    - fastlane $scheme
  artifacts:
    expire_in: 30 days
    paths:
      - build

但是我的管道失败了，日志中出现了给定的错误

Running with gitlab-runner 13.8.0 (775dd39d)
  on ClaimIt CI runner wHJuZbdb
Preparing the "shell" executor
00:00
Using Shell executor...
Preparing environment
00:01
Running on macmini-57.macweb.com...
Getting source from Git repository
00:00
Fetching changes...
Reinitialized existing Git repository in /Users/cloud/Desktop/ClaimIt/ClaimIt-iOS-new/builds/wHJuZbdb/0/Protovate/ClaimIt-iOS-new/.git/
Cleaning up file based variables
00:00
ERROR: Job failed: exit status 1

---

请告知。

您找到了解决此问题的方法吗？