siyuan-note/siyuan · warning

variable %q contains NUL

Error message

variable %q contains NUL

What it means

Validation error from validateMCPServerEnvironment: an explicit Env value contains a NUL byte (\x00). NUL cannot appear in a C environ entry and would silently truncate the value when passed to the child. The offending variable name is quoted via %q so you can locate it.

Source

Thrown at kernel/mcp/client/mcp.go:562

func validateMCPServerEnvironment(server conf.MCPServer, goos string) error {
	inherited := map[string]bool{}
	for _, name := range server.InheritEnv {
		if err := validateEnvironmentName(name); err != nil {
			return err
		}
		key := environmentKey(name, goos)
		if inherited[key] {
			return fmt.Errorf("duplicate inherited variable %q", name)
		}
		inherited[key] = true
	}
	explicit := map[string]bool{}
	for name, value := range server.Env {
		if err := validateEnvironmentName(name); err != nil {
			return err
		}
		if strings.ContainsRune(value, '\x00') {
			return fmt.Errorf("variable %q contains NUL", name)
		}
		key := environmentKey(name, goos)
		if explicit[key] {
			return fmt.Errorf("duplicate variable %q", name)
		}
		explicit[key] = true
	}
	return nil
}

// ValidateMCPServerEnvironment 校验当前平台上的 stdio 环境变量配置。
func ValidateMCPServerEnvironment(server conf.MCPServer) error {
	return validateMCPServerEnvironment(server, runtime.GOOS)
}

func defaultMCPEnvironmentNames(goos string) []string {
	if goos == "windows" {
		return []string{"APPDATA", "HOMEDRIVE", "HOMEPATH", "LOCALAPPDATA", "PATH", "PATHEXT",

View on GitHub (pinned to 251596fc0d)

Solutions

1. Locate the variable named in the error message and rewrite its value without NUL bytes.
2. If the value comes from model.Conf.Secrets / Variables via ResolveSecretsVars, inspect the source of that secret for corruption.
3. Strip NUL bytes programmatically before writing the config: strings.ReplaceAll(value, "\x00", "").

Example fix

// before (value contains a stray NUL)
"env": {"TOKEN": "abc\u0000def"}
// after
"env": {"TOKEN": "abcdef"}

import "strings"
func sanitizeEnvValue(v string) string {
    return strings.ReplaceAll(v, "\x00", "")
}

When it happens

Trigger: Iterating server.Env, validateMCPServerEnvironment runs strings.ContainsRune(value, '\x00') on each value; if a value contains a NUL byte, this error is returned for the corresponding name.

Common situations: Value was read from a binary file or pasted from a terminal that embedded a control character; secret material loaded from a corrupted credential store; mistaken use of a byte slice containing a trailing NUL (e.g. C-go interop residue).

Related errors

• environment: %w
• name is empty
• invalid name %q
• duplicate inherited variable %q
• duplicate variable %q

AI-assisted analysis of siyuan-note/siyuan@251596fc0d (2026-08-12). Data as JSON: /api/errors/2afc1a34bb3a7558. Report an issue: GitHub.