docker/cli · error

type is empty: must be one of

Error message

type is empty: must be one of "%s"

What it means

Returned by 'docker inspect' when --type is explicitly set but its value is empty (e.g. --type ''). The command requires a non-empty value drawn from the supported object types when the flag is present.

Solutions

1. Provide a concrete type from: container, image, network, node, plugin, secret, service, task, volume (or config).
2. If you don't want to filter by type, omit --type entirely.
3. Validate the variable is non-empty before passing it.

Example fix

# before
OBJ_TYPE=""
docker inspect --type "$OBJ_TYPE" myid

# after
OBJ_TYPE=container
docker inspect --type "$OBJ_TYPE" myid
# -or- omit the flag
docker inspect myid

// Reject empty --type when the flag is present
if cmd.Flags().Changed("type") && opts.objectType == "" {
    return errors.New("--type must not be empty")
}

func nonEmptyType(s string) bool {
	return strings.TrimSpace(s) != ""
}

When it happens

Trigger: Running 'docker inspect --type "" <id>' or passing an empty --type from a script/variable. The guard at inspect.go:68-70 checks flags.Changed("type") && opts.objectType == "".

Common situations: Shell variable expanded to empty ('$OBJ_TYPE' unset); typo '--type=' with nothing after; template/script bug feeding an empty type.

Related errors

• unknown type: : must be one of
• other flags may not be combined with --rollback
• specify only one -H
• `-- ` flag requires the `--rotate` flag to update the CA
• error: no such object

AI-assisted analysis of docker/cli@4f84911bfe (2026-08-07). Data as JSON: /api/errors/3a1e7fe819dd998c. Report an issue: GitHub.

Appendix: source

Thrown at cli/command/system/inspect.go:69

type inspectOptions struct {
	format     string
	objectType objectType
	size       bool
	ids        []string
}

// newInspectCommand creates a new cobra.Command for `docker inspect`
func newInspectCommand(dockerCLI command.Cli) *cobra.Command {
	var opts inspectOptions

	cmd := &cobra.Command{
		Use:   "inspect [OPTIONS] NAME|ID [NAME|ID...]",
		Short: "Return low-level information on Docker objects",
		Args:  cli.RequiresMinArgs(1),
		RunE: func(cmd *cobra.Command, args []string) error {
			opts.ids = args
			if cmd.Flags().Changed("type") && opts.objectType == "" {
				return fmt.Errorf(`type is empty: must be one of "%s"`, strings.Join(allTypes, `", "`))
			}
			return runInspect(cmd.Context(), dockerCLI, opts)
		},
		// TODO(thaJeztah): should we consider adding completion for common object-types? (images, containers?)
		ValidArgsFunction:     completeObjectNames(dockerCLI),
		DisableFlagsInUseLine: true,
	}

	flags := cmd.Flags()
	flags.StringVarP(&opts.format, "format", "f", "", flagsHelper.InspectFormatHelp)
	flags.StringVar(&opts.objectType, "type", "", "Only inspect objects of the given type")
	flags.BoolVarP(&opts.size, "size", "s", false, "Display total file sizes if the type is container")

	_ = cmd.RegisterFlagCompletionFunc("type", completion.FromList(allTypes...))

	return cmd
}

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