Error in bundle causes juju to panic

Upon deployment of a bundle with a syntax error, juju panicked.

The error in the bundle was an empty charm. Look at the coredns line:
```
  kubernetes-master:
    bindings:
      ? ''
      : oam-space
      certificates: internal-space
      kube-api-endpoint: internal-space
      kube-control: internal-space
      loadbalancer: internal-space
      cni: k8s-pods-space
    charm: cs:~containers/kubernetes-master
    num_units: 3
    options:
      allow-privileged: 'true'
      authorization-mode: RBAC,Node
      # dns-provider: node
  coredns:

  kubernetes-worker:
    bindings:
      ? ''
      : oam-space
      certificates: internal-space
      kube-control: internal-space
      cni: k8s-pods-space
    charm: cs:~containers/kubernetes-worker
    expose: true
    num_units: 3
    options:
      allow-privileged: 'true'
```

traceback :
ubuntu@infra-01:~/$ fce build --layer lmacmr [78/78]
2021-03-11-22:32:33 root WARNING ["There must be at least three zones and there must be odd number of zones. Zones found: {'zone1'}"]
2021-03-11-22:32:33 fce.build INFO Started building layer: lmacmr
2021-03-11-22:32:33 fce.juju_workload INFO Starting step: lmacmr:create_model
2021-03-11-22:32:34 fce.juju_workload INFO Finished step: lmacmr:create_model. Time elapsed (hh:mm:ss.ms): 0:00:00.905820
2021-03-11-22:32:34 fce.juju_workload INFO Starting step: lmacmr:set_model_config
2021-03-11-22:32:34 fce.juju_workload INFO Finished step: lmacmr:set_model_config. Time elapsed (hh:mm:ss.ms): 0:00:00.214416
2021-03-11-22:32:34 fce.juju_workload INFO Starting step: lmacmr:ensure_storage_pools
2021-03-11-22:32:34 fce.juju_workload INFO Finished step: lmacmr:ensure_storage_pools. Time elapsed (hh:mm:ss.ms): 0:00:00.306996
2021-03-11-22:32:34 fce.juju_workload INFO Starting step: lmacmr:add_manual_machines
2021-03-11-22:32:34 fce.juju_workload INFO Finished step: lmacmr:add_manual_machines. Time elapsed (hh:mm:ss.ms): 0:00:00.000012
2021-03-11-22:32:34 fce.juju_workload INFO Starting step: lmacmr:deploy_bundle
2021-03-11 22:32:35.077297 22:32:35 INFO juju.cmd supercommand.go:54 running juju [2.8.9 0 a48bedf0ae2096d0cf750b7676da9b0a994cff09 gc go1.14.15]
2021-03-11 22:32:35.077398 22:32:35 DEBUG juju.cmd supercommand.go:55 args: []string{"/snap/juju/15523/bin/juju", "deploy", "-m", "foundations-maas:kubernetes", "--debug", "./config/../generated/kubernetes/bun
dle.yaml", "--overlay", "./config/overlay_kubernetes_options.yaml", "--overlay", "./config/overlay_kubernetes_placement.yaml", "--overlay", "./config/overlay_kubernetes_versioned.yaml", "--overlay", "./config/ov
erlay_kubernetes_saas.yaml"}
2021-03-11 22:32:35.078217 22:32:35 INFO juju.juju api.go:67 connecting to API addresses: [172.24.70.19:17070 172.24.70.20:17070 172.24.70.21:17070]
2021-03-11 22:32:35.100555 22:32:35 DEBUG juju.api apiclient.go:1107 successfully dialed "wss://172.24.70.19:17070/api"
2021-03-11 22:32:35.100596 22:32:35 INFO juju.api apiclient.go:639 connection established to "wss://172.24.70.19:17070/api"
2021-03-11 22:32:35.142810 22:32:35 INFO juju.juju api.go:67 connecting to API addresses: [172.24.70.19:17070 172.24.70.20:17070 172.24.70.21:17070]
2021-03-11 22:32:35.154207 22:32:35 DEBUG juju.api apiclient.go:1107 successfully dialed "wss://172.24.70.19:17070/model/a24e3392-b509-4b33-8cb3-3245d99b5f83/api"
2021-03-11 22:32:35.154304 22:32:35 INFO juju.api apiclient.go:639 connection established to "wss://172.24.70.19:17070/model/a24e3392-b509-4b33-8cb3-3245d99b5f83/api"
2021-03-11 22:32:35.196554 22:32:35 INFO juju.juju api.go:67 connecting to API addresses: [172.24.70.19:17070 172.24.70.20:17070 172.24.70.21:17070]
2021-03-11 22:32:35.215834 22:32:35 DEBUG juju.api apiclient.go:1107 successfully dialed "wss://172.24.70.21:17070/api"
2021-03-11 22:32:35.215906 22:32:35 INFO juju.api apiclient.go:639 connection established to "wss://172.24.70.21:17070/api"
2021-03-11 22:32:35.255197 22:32:35 INFO juju.juju api.go:302 API endpoints changed from [172.24.70.21:17070 172.24.70.20:17070 172.24.70.19:17070] to [172.24.70.21:17070 172.24.70.19:17070 172.24.70.20:17070]
2021-03-11 22:32:35.267203 22:32:35 DEBUG juju.api monitor.go:35 RPC connection died
2021-03-11 22:32:35.269840 panic: runtime error: invalid memory address or nil pointer dereference
2021-03-11 22:32:35.269906 [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x9ba3b5]
2021-03-11 22:32:35.269924
2021-03-11 22:32:35.269939 goroutine 1 [running]:
2021-03-11 22:32:35.269960 github.com/juju/charm/v7.ReadAndMergeBundleData(0xc000a89980, 0x5, 0x8, 0x4, 0x5, 0xc000a89980)
2021-03-11 22:32:35.269984 /build/snapcraft-juju-35d6cf/parts/juju/src/vendor/github.com/juju/charm/v7/overlay.go:443 +0x7a5
2021-03-11 22:32:35.270002 github.com/juju/juju/cmd/juju/application.composeAndVerifyBundle(0x4528180, 0xc000a9e7b0, 0xc0008a9040, 0x4, 0x4, 0x0, 0xc000f4f410, 0xffffffffffffffff)
2021-03-11 22:32:35.270020 /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/application/bundle.go:137 +0x17d
2021-03-11 22:32:35.270037 github.com/juju/juju/cmd/juju/application.(*DeployCommand).deployBundle(0xc00020fb80, 0xc00089b5e0, 0x0, 0x4528180, 0xc000a9e7b0, 0x0, 0x0, 0x0, 0xc0008a9040, 0x4, ...)
2021-03-11 22:32:35.270054 /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/application/deploy.go:898 +0x36f
2021-03-11 22:32:35.270070 github.com/juju/juju/cmd/juju/application.(*DeployCommand).maybeReadLocalBundle.func1(0xc00089b5e0, 0x45da6c0, 0xc000552500, 0x3e51548, 0xc000198e40, 0x0, 0x0)
2021-03-11 22:32:35.270087 /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/application/deploy.go:1373 +0x1c0
2021-03-11 22:32:35.270107 github.com/juju/juju/cmd/juju/application.(*DeployCommand).Run(0xc00020fb80, 0xc00089b5e0, 0x0, 0x0)
2021-03-11 22:32:35.270121 /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/application/deploy.go:1197 +0x4c2
2021-03-11 22:32:35.270134 github.com/juju/juju/cmd/modelcmd.(*modelCommandWrapper).Run(0xc00097b080, 0xc00089b5e0, 0x6552be0, 0x3326b80)
2021-03-11 22:32:35.270148 /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/modelcmd/modelcommand.go:623 +0x129
2021-03-11 22:32:35.270162 github.com/juju/juju/cmd/modelcmd.(*baseCommandWrapper).Run(0xc000891d80, 0xc00089b5e0, 0x0, 0x0)
2021-03-11 22:32:35.270175 /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/modelcmd/base.go:493 +0xa8
2021-03-11 22:32:35.270188 github.com/juju/cmd.(*SuperCommand).Run(0xc000658a00, 0xc00089b5e0, 0xc00089b5e0, 0x0)
2021-03-11 22:32:35.270206 /build/snapcraft-juju-35d6cf/parts/juju/src/vendor/github.com/juju/cmd/supercommand.go:523 +0x2ba
2021-03-11 22:32:35.270230 github.com/juju/cmd.Main(0x456a6a0, 0xc000658a00, 0xc00089b5e0, 0xc000b15930, 0xd, 0xd, 0xc000658a00)
2021-03-11 22:32:35.270246 /build/snapcraft-juju-35d6cf/parts/juju/src/vendor/github.com/juju/cmd/cmd.go:387 +0x2bf
2021-03-11 22:32:35.270262 github.com/juju/juju/cmd/juju/commands.main.Run(0x3e53fd8, 0xc00004c0e0, 0xe, 0xe, 0xc0007b0920)
2021-03-11 22:32:35.270278 /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/commands/main.go:169 +0x46e
2021-03-11 22:32:35.270294 github.com/juju/juju/cmd/juju/commands.Main(...)
2021-03-11 22:32:35.270310 /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/commands/main.go:90
2021-03-11 22:32:35.270325 main.main()
2021-03-11 22:32:35.270341 /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/main.go:37 +0xb9
2021-03-11-22:32:35 root ERROR [localhost] Command failed: juju deploy -m foundations-maas:kubernetes --debug ./config/../generated/kubernetes/bundle.yaml --overlay ./config/overlay_kubernetes_options.yaml --ove
rlay ./config/overlay_kubernetes_placement.yaml --overlay ./config/overlay_kubernetes_versioned.yaml --overlay ./config/overlay_kubernetes_saas.yaml
2021-03-11-22:32:35 root ERROR [localhost] STDOUT follows:
22:32:35 INFO juju.cmd supercommand.go:54 running juju [2.8.9 0 a48bedf0ae2096d0cf750b7676da9b0a994cff09 gc go1.14.15]
22:32:35 DEBUG juju.cmd supercommand.go:55 args: []string{"/snap/juju/15523/bin/juju", "deploy", "-m", "foundations-maas:kubernetes", "--debug", "./config/../generated/kubernetes/bundle.yaml", "--overlay", "./
config/overlay_kubernetes_options.yaml", "--overlay", "./config/overlay_kubernetes_placement.yaml", "--overlay", "./config/overlay_kubernetes_versioned.yaml", "--overlay", "./config/overlay_kubernetes_saas.yaml"
}
22:32:35 INFO juju.juju api.go:67 connecting to API addresses: [172.24.70.19:17070 172.24.70.20:17070 172.24.70.21:17070]
22:32:35 DEBUG juju.api apiclient.go:1107 successfully dialed "wss://172.24.70.19:17070/api"
22:32:35 INFO juju.api apiclient.go:639 connection established to "wss://172.24.70.19:17070/api"
22:32:35 INFO juju.juju api.go:67 connecting to API addresses: [172.24.70.19:17070 172.24.70.20:17070 172.24.70.21:17070]
22:32:35 DEBUG juju.api apiclient.go:1107 successfully dialed "wss://172.24.70.19:17070/model/a24e3392-b509-4b33-8cb3-3245d99b5f83/api"
22:32:35 INFO juju.api apiclient.go:639 connection established to "wss://172.24.70.19:17070/model/a24e3392-b509-4b33-8cb3-3245d99b5f83/api"
22:32:35 INFO juju.juju api.go:67 connecting to API addresses: [172.24.70.19:17070 172.24.70.20:17070 172.24.70.21:17070]
22:32:35 DEBUG juju.api apiclient.go:1107 successfully dialed "wss://172.24.70.21:17070/api"
22:32:35 INFO juju.api apiclient.go:639 connection established to "wss://172.24.70.21:17070/api"
22:32:35 INFO juju.juju api.go:302 API endpoints changed from [172.24.70.21:17070 172.24.70.20:17070 172.24.70.19:17070] to [172.24.70.21:17070 172.24.70.19:17070 172.24.70.20:17070]
22:32:35 DEBUG juju.api monitor.go:35 RPC connection died
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x9ba3b5]

goroutine 1 [running]:
github.com/juju/charm/v7.ReadAndMergeBundleData(0xc000a89980, 0x5, 0x8, 0x4, 0x5, 0xc000a89980)
        /build/snapcraft-juju-35d6cf/parts/juju/src/vendor/github.com/juju/charm/v7/overlay.go:443 +0x7a5
github.com/juju/juju/cmd/juju/application.composeAndVerifyBundle(0x4528180, 0xc000a9e7b0, 0xc0008a9040, 0x4, 0x4, 0x0, 0xc000f4f410, 0xffffffffffffffff)
        /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/application/bundle.go:137 +0x17d
github.com/juju/juju/cmd/juju/application.(*DeployCommand).deployBundle(0xc00020fb80, 0xc00089b5e0, 0x0, 0x4528180, 0xc000a9e7b0, 0x0, 0x0, 0x0, 0xc0008a9040, 0x4, ...)
        /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/application/deploy.go:898 +0x36f
github.com/juju/juju/cmd/juju/application.(*DeployCommand).maybeReadLocalBundle.func1(0xc00089b5e0, 0x45da6c0, 0xc000552500, 0x3e51548, 0xc000198e40, 0x0, 0x0)
        /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/application/deploy.go:1373 +0x1c0
github.com/juju/juju/cmd/juju/application.(*DeployCommand).Run(0xc00020fb80, 0xc00089b5e0, 0x0, 0x0)
        /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/application/deploy.go:1197 +0x4c2
github.com/juju/juju/cmd/modelcmd.(*modelCommandWrapper).Run(0xc00097b080, 0xc00089b5e0, 0x6552be0, 0x3326b80)
        /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/modelcmd/modelcommand.go:623 +0x129
github.com/juju/juju/cmd/modelcmd.(*baseCommandWrapper).Run(0xc000891d80, 0xc00089b5e0, 0x0, 0x0)
        /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/modelcmd/base.go:493 +0xa8
github.com/juju/cmd.(*SuperCommand).Run(0xc000658a00, 0xc00089b5e0, 0xc00089b5e0, 0x0)
        /build/snapcraft-juju-35d6cf/parts/juju/src/vendor/github.com/juju/cmd/supercommand.go:523 +0x2ba
github.com/juju/cmd.Main(0x456a6a0, 0xc000658a00, 0xc00089b5e0, 0xc000b15930, 0xd, 0xd, 0xc000658a00)
        /build/snapcraft-juju-35d6cf/parts/juju/src/vendor/github.com/juju/cmd/cmd.go:387 +0x2bf
github.com/juju/juju/cmd/juju/commands.main.Run(0x3e53fd8, 0xc00004c0e0, 0xe, 0xe, 0xc0007b0920)
        /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/commands/main.go:169 +0x46e
github.com/juju/juju/cmd/juju/commands.Main(...)
        /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/commands/main.go:90
main.main()
        /build/snapcraft-juju-35d6cf/parts/juju/src/cmd/juju/main.go:37 +0xb9
2021-03-11-22:32:35 root ERROR [localhost] STDERR follows:
None
Traceback (most recent call last):
  File "/usr/local/bin/fce", line 11, in <module>
    load_entry_point('foundationcloudengine', 'console_scripts', 'fce')()
  File "/home/ubuntu/cpe-foundation/foundationcloudengine/foundationcloudengine/main.py", line 170, in entry_point
    sys.exit(main(sys.argv[1:]))
  File "/home/ubuntu/cpe-foundation/foundationcloudengine/foundationcloudengine/main.py", line 161, in main
    opts.func(opts)
  File "/home/ubuntu/cpe-foundation/foundationcloudengine/foundationcloudengine/build.py", line 107, in build_main
    build_and_validate_if_needed(
  File "/home/ubuntu/cpe-foundation/foundationcloudengine/foundationcloudengine/build.py", line 75, in build_and_validate_if_needed
    layer.build_outer(only_steps)
  File "/home/ubuntu/cpe-foundation/foundationcloudengine/foundationcloudengine/layers/baselayer.py", line 122, in build_outer
    self.build(only_steps=only_steps)
  File "/home/ubuntu/cpe-foundation/foundationcloudengine/foundationcloudengine/layers/jujuworkloadlayer.py", line 901, in build
    self.run_steps(only_steps)
  File "/home/ubuntu/cpe-foundation/foundationcloudengine/foundationcloudengine/layers/steppedbaselayer.py", line 114, in run_steps
    step.build()
  File "/home/ubuntu/cpe-foundation/foundationcloudengine/foundationcloudengine/layers/jujuworkloadlayer.py", line 679, in build
    deploy(
  File "/home/ubuntu/cpe-foundation/foundationcloudengine/foundationcloudengine/juju_cli.py", line 201, in deploy
    local(command, stderr=subprocess.STDOUT, output_mode="live")
  File "/home/ubuntu/cpe-foundation/foundationcloudengine/foundationcloudengine/remotehelpers.py", line 209, in local
    return run_cmd(cmd, target_machine, **kwargs)
  File "/home/ubuntu/cpe-foundation/foundationcloudengine/foundationcloudengine/remotehelpers.py", line 147, in run_cmd
    raise subprocess.CalledProcessError(ps.returncode, cmd, output=out, stderr=err)
subprocess.CalledProcessError: Command '['juju', 'deploy', '-m', 'foundations-maas:kubernetes', '--debug', './config/../generated/kubernetes/bundle.yaml', '--overlay', './config/overlay_kubernetes_options.yaml',
 '--overlay', './config/overlay_kubernetes_placement.yaml', '--overlay', './config/overlay_kubernetes_versioned.yaml', '--overlay', './config/overlay_kubernetes_saas.yaml']' returned non-zero exit status 2.