ko builder fails on empty ldflags

[briandealwis]

Playing around with github.com/gardener/gardener to try to reproduce reported problems. This repository uses a helper script to set an environment variable LD_FLAGS which is used by the Ko builds:

build:
  artifacts:
  - image: eu.gcr.io/gardener-project/gardener/apiserver
    ko:
      main: ./cmd/gardener-apiserver
      ldflags:
      - "{{.LD_FLAGS}}"
      dependencies:
        paths:

Expected behavior

When LD_FLAGS is unset, the build should skip.

Actual behavior

Building [eu.gcr.io/gardener-project/gardener/seed-admission-controller]...
Target platforms: [linux/arm64]
Using base gcr.io/distroless/static:nonroot@sha256:ed05c7a5d67d6beebeba19c6b9082a5513d5f9c3e22a883b9dc73ec39ba41c04 for github.com/gardener/gardener/cmd/gardener-seed-admission-controller
Using build config eu.gcr.io/gardener-project/gardener/seed-admission-controller for github.com/gardener/gardener/cmd/gardener-seed-admission-controller
Building github.com/gardener/gardener/cmd/gardener-seed-admission-controller for linux/arm64
Unexpected error running "go build": exit status 2
invalid value "<no value>" for flag -ldflags: missing =<value> in <pattern>=<value>
usage: go build [-o output] [build flags] [packages]
Run 'go help build' for details.
Building [eu.gcr.io/gardener-project/gardener/scheduler]...

Information

• Skaffold version: HEAD
• Operating system: macOS arm64

<paste your skaffold.yaml here>

Steps to reproduce the behavior

1. github.com/gardener/gardener
2. skaffold debug

[aaron-prindle]

tagging @halvards