fix nil pointer

[jkhelil]

Changes

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Has Docs included if any changes are user facing
• Has Tests included if any functionality added or changed
• Follows the commit message standard
• Meets the Tekton contributor standards (including
  functionality, content, code)
• Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings)
• Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

NONE

[vdemeester]

cc @lcarva
/lgtm

[vdemeester]

/cherry-pick release-v0.23.x

[tekton-robot]

@vdemeester: once the present PR merges, I will cherry-pick it on top of release-v0.23.x in a new PR and assign it to you.

In response to this:

/cherry-pick release-v0.23.x

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[lcarva]

/lgtm

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lcarva, vdemeester

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• OWNERS [lcarva]

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[lcarva]

/retest

[jkhelil]

/retest

[jkhelil]

/retest

[vdemeester]

/retest

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-chains-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/chains/formats/slsa/v1/pipelinerun/pipelinerun.go	75.9%	74.4%	-1.4

[tekton-robot]

@vdemeester: new pull request created: #1249

In response to this:

/cherry-pick release-v0.23.x

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.