Gitlab CI Cleaning up file based variables Error: exit status 1

I am using fastlane with Gitlab CI to build iOS projects. GItlab-runner runs as shell. Here is the yml file.

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

But my pipelines fails with the given error in logs

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

Please advise.