fix: prevent nil pointer dereference when config file is missing

[wangke19]

Fixed by AI Cursor.

Problem

The commitchecker tool was panicking with a nil pointer dereference when the config file (commitchecker.yaml) was not present. This happened because:

1. The Load function returns nil, nil when the config file doesn't exist (expected behavior)
2. The code was trying to print the config without checking if it was nil first
3. There was also a potential issue where cfg fields were accessed without nil checks

Solution

• Added nil check before printing config to prevent panic
• Added nil check before accessing cfg fields in merge-base logic
• Gracefully handle missing config file with informative message

Testing

• Built and tested the fix locally
• Confirmed the program no longer panics when config file is missing
• Program now displays "config: (no config file found)" instead of crashing

Changes

• commitchecker/commitchecker.go: Added nil checks for config handling

Fixes the panic: runtime error: invalid memory address or nil pointer dereference at commitchecker.go:31 when commitchecker.yaml is not present.

[openshift-ci]

@wangke19: This PR was included in a payload test run from openshift/kubernetes#2475
trigger 0 job(s) for the /payload-(with-prs|job|aggregate|job-with-prs|aggregate-with-prs) command

[wangke19]

/payload-job-with-prs pull-ci-openshift-build-machinery-go-master-verify-commitchecker openshift/kubernetes#2475

[openshift-ci]

@wangke19: the repo openshift/build-machinery-go does not contribute to the OpenShift official images, or the base branch is not currently having images promoted

[openshift-ci]

@wangke19: This PR was included in a payload test run from openshift/kubernetes#2475
trigger 0 job(s) for the /payload-(with-prs|job|aggregate|job-with-prs|aggregate-with-prs) command

[openshift-ci]

@wangke19: all tests passed!

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[jsafrane]

@wangke19 can you please link PR where commitchecker failed?

I can see it crashing in one of my PRs https://prow.ci.openshift.org/view/gs/test-platform-results/pr-logs/pull/openshift_aws-ebs-csi-driver/294/pull-ci-openshift-aws-ebs-csi-driver-master-verify-commits/1980993927829786624

But that uses commitchecker verson v0.0.0-unknown-c3556e1, which does not include #109

[jsafrane]

Not sure how to convince CI to refresh the image

[jsafrane]

I don't think this PR fixes anything, the null pointer dereference is already fixed. But I am going to merge it to see if a new commitchecker image gets pushed to the right places.
/lgtm
/approve

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jsafrane, wangke19

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[jsafrane]

From some reason a new image with this PR was pushed to the right places in few hours
/shrug