packer-plugin-nspawn crash https://github.com/jboero/packer-plugin-nspawn/issues/15

crash.log

2023/05/27 11:55:08 [INFO] Packer version: 1.8.6 [go1.20.4 linux amd64]
2023/05/27 11:55:08 Old default config directory found: /home/rickard/.packer.d
2023/05/27 11:55:08 [TRACE] discovering plugins in /home/linuxbrew/.linuxbrew/Cellar/packer/1.8.7/libexec/bin
2023/05/27 11:55:08 Old default config directory found: /home/rickard/.packer.d
2023/05/27 11:55:08 [TRACE] discovering plugins in /home/rickard/.packer.d/plugins
2023/05/27 11:55:08 [DEBUG] Discovered plugin: nspawn = /home/rickard/.packer.d/plugins/packer-plugin-nspawn
2023/05/27 11:55:08 [INFO] found external [machine] builders from nspawn plugin
2023/05/27 11:55:08 found external [images] datasource from nspawn plugin
2023/05/27 11:55:08 [TRACE] discovering plugins in .
2023/05/27 11:55:08 [TRACE] discovering plugins in 
2023/05/27 11:55:08 [TRACE] discovering plugins in /home/linuxbrew/.linuxbrew/bin
2023/05/27 11:55:08 [INFO] PACKER_CONFIG env var not set; checking the default config file path
2023/05/27 11:55:08 [INFO] PACKER_CONFIG env var set; attempting to open config file: /home/rickard/.packerconfig
2023/05/27 11:55:08 [WARN] Config file doesn't exist: /home/rickard/.packerconfig
2023/05/27 11:55:08 Old default config directory found: /home/rickard/.packer.d
2023/05/27 11:55:08 [INFO] Setting cache directory: /home/rickard/.cache/packer
2023/05/27 11:55:08 Old default config directory found: /home/rickard/.packer.d
2023/05/27 11:55:08 [TRACE] Starting external plugin /home/rickard/.packer.d/plugins/packer-plugin-nspawn start builder machine
2023/05/27 11:55:08 Starting plugin: /home/rickard/.packer.d/plugins/packer-plugin-nspawn []string{"/home/rickard/.packer.d/plugins/packer-plugin-nspawn", "start", "builder", "machine"}
2023/05/27 11:55:08 Waiting for RPC address for: /home/rickard/.packer.d/plugins/packer-plugin-nspawn
2023/05/27 11:55:08 Received unix RPC address for /home/rickard/.packer.d/plugins/packer-plugin-nspawn: addr is /tmp/packer-plugin262930468
2023/05/27 11:55:08 packer-plugin-nspawn plugin: 2023/05/27 11:55:08 Plugin address: unix /tmp/packer-plugin262930468
2023/05/27 11:55:08 packer-plugin-nspawn plugin: 2023/05/27 11:55:08 Waiting for connection...
2023/05/27 11:55:08 packer-plugin-nspawn plugin: 2023/05/27 11:55:08 Serving a plugin connection...
2023/05/27 11:55:08 packer-plugin-nspawn plugin: 2023/05/27 11:55:08 [TRACE] starting builder machine
2023/05/27 11:55:08 ConfigSpec failed: gob: type cty.Type has no exported fields
2023/05/27 11:55:08 waiting for all plugin processes to complete...
2023/05/27 11:55:08 /home/rickard/.packer.d/plugins/packer-plugin-nspawn: plugin process exited
panic: ConfigSpec failed: gob: type cty.Type has no exported fields [recovered]
	panic: ConfigSpec failed: gob: type cty.Type has no exported fields

goroutine 1 [running]:
log.Panic({0xc000a9e758?, 0x8f34a80?, 0xc000a9e7b8?})
	log/log.go:384 +0x65
github.com/hashicorp/packer/packer.(*cmdBuilder).checkExit(0x417f70?, {0x42476a0, 0xc000378080}, 0x0)
	github.com/hashicorp/packer/packer/cmd_builder.go:47 +0x7f
github.com/hashicorp/packer/packer.(*cmdBuilder).ConfigSpec.func1()
	github.com/hashicorp/packer/packer/cmd_builder.go:19 +0x39
panic({0x42476a0, 0xc000378080})
	runtime/panic.go:884 +0x213
github.com/hashicorp/packer-plugin-sdk/rpc.(*commonClient).ConfigSpec(0xc0003b45a0)
	github.com/hashicorp/packer-plugin-sdk@v0.4.0/rpc/common.go:47 +0x297
github.com/hashicorp/packer/packer.(*cmdBuilder).ConfigSpec(0x0?)
	github.com/hashicorp/packer/packer/cmd_builder.go:22 +0x65
github.com/hashicorp/packer/hcl2template.decodeHCL2Spec({0x5a55f30, 0xc000c38990}, 0x52a6e54?, {0x7f56d8a4a6a0?, 0xc000013020?})
	github.com/hashicorp/packer/hcl2template/decode.go:17 +0x39
github.com/hashicorp/packer/hcl2template.(*PackerConfig).startBuilder(0xc0003e9900, {{{0xc0006e25a7, 0xe}, {0xc0006e25b6, 0xd}}, {0x0, 0x0}, {0x5a55f30, 0xc000c38990}}, 0xc000c403d8)
	github.com/hashicorp/packer/hcl2template/types.source.go:117 +0x1cd
github.com/hashicorp/packer/hcl2template.(*PackerConfig).GetBuilds(0xc0003e9900, {{0x0, 0x0, 0x0}, {0x0, 0x0, 0x0}, 0x0, 0x0, {0x0, ...}, ...})
	github.com/hashicorp/packer/hcl2template/types.packer_config.go:662 +0xf10
github.com/hashicorp/packer/command.(*BuildCommand).RunContext(0xc000a2ab40, {0x5a556a8?, 0xc0000d60f0}, 0xc000348ab0)
	github.com/hashicorp/packer/command/build.go:110 +0x23d
github.com/hashicorp/packer/command.(*BuildCommand).Run(0xc000a2ab40, {0xc00011a170, 0x1, 0x1})
	github.com/hashicorp/packer/command/build.go:38 +0xc5
github.com/mitchellh/cli.(*CLI).Run(0xc00038e140)
	github.com/mitchellh/cli@v1.1.2/cli.go:262 +0x5f8
main.wrappedMain()
	github.com/hashicorp/packer/main.go:262 +0xcc5
main.realMain()
	github.com/hashicorp/packer/main.go:49 +0xf5
main.main()
	github.com/hashicorp/packer/main.go:35 +0x19