[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Elvand-Lie
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Hi @Elvand-Lie. Thanks for your PR.

I'm waiting for a knative member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Verification Evidence

1. go vet: clean

$ go vet ./pkg/functions
# (no output, clean)

2. Before vs After

f := fn.Function{Build: fn.BuildSpec{Image: ""}}

// BEFORE fix:
f.ImageNameWithDigest("sha256:abc123")
// produces "@sha256:abc123", which is an INVALID OCI reference (no image name before @)
// Downstream: name.ParseReference("@sha256:abc123") fails with "could not parse reference"

// AFTER fix:
f.ImageNameWithDigest("sha256:abc123")
// produces "", a safe empty string that callers can check and handle gracefully

3. Code path trace showing how you hit this bug

client.go:Push()
  calls pusher.Push(), which returns imageDigest
  then client.go:1275 sets f.Build.Image = f.ImageNameWithDigest(imageDigest)
    if Build.Image was "" (interrupted build, corrupt func.yaml),
    this produces "@sha256:..." which fails all subsequent operations

4. Existing test suite, all pass

$ go test ./pkg/functions/ -run TestFunction_ImageWithDigest -count=1 -v
=== RUN   TestFunction_ImageWithDigest
=== RUN   TestFunction_ImageWithDigest/Full_path_with_port
=== RUN   TestFunction_ImageWithDigest/Path_with_namespace
=== RUN   TestFunction_ImageWithDigest/Just_image_name
=== RUN   TestFunction_ImageWithDigest/Full_path_with_port_and_SHA256_Digest
=== RUN   TestFunction_ImageWithDigest/Full_path_with_port_and_SHA256_Digest_with_empty_ImageDigest
--- PASS: TestFunction_ImageWithDigest (0.00s)
PASS
ok  	knative.dev/func/pkg/functions	0.394s

5. The fix (3 lines)

 image := f.Build.Image
+if image == "" {
+    return ""
+}

Minimal and defensive. No behavior change for any non-empty image path.

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 51.68%. Comparing base (813791a) to head (b75d85e).

@@            Coverage Diff             @@
##             main    #3905      +/-   ##
==========================================
- Coverage   53.93%   51.68%   -2.26%     
==========================================
  Files         200      200              
  Lines       23681    23682       +1     
==========================================
- Hits        12772    12239     -533     
- Misses       9674    10302     +628     
+ Partials     1235     1141      -94     

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