## What this PR does
Some HelmReleases use `chartRef` instead of `chart`. If the lineage
webhook finds such a HelmRelease, a nil pointer dereference happens.
This patch adds a nil check to guard against this.
### Release note
```release-note
[lineage] Add a nil check to guard against HelmReleases with a nil
.spec.chart field when traversing the ownership tree.
```
(cherry picked from commit
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| .. | ||
| config.go | ||
| controller.go | ||
| matcher.go | ||
| types.go | ||
| webhook.go | ||