symfony/http-foundation · error · InvalidArgumentException

At least one separator must be specified.

Error message

At least one separator must be specified.

What it means

An InvalidArgumentException raised by HeaderUtils::split() when its $separators argument is an empty string. split() builds a regex character class from the separator characters and cannot split on nothing, so an empty separator list is a programming error detected before any parsing happens; the header string itself is irrelevant here.

Solutions

1. Pass at least one separator character, e.g. HeaderUtils::split($header, ',;')
2. Validate $separators is non-empty before calling split()
3. Return or process the header unsplit (e.g. explode on a known delimiter) when no separators apply

When it happens

Trigger: Thrown at HeaderUtils.php:48 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of symfony/http-foundation@5aea19cd67 (2026-09-13). Data as JSON: /api/errors/d8ba0d1cee242176. Report an issue: GitHub.

Appendix: source

Thrown at HeaderUtils.php:48

    public static function split(string $header, string $separators): array
    {
        if ('' === $separators) {
            throw new \InvalidArgumentException('At least one separator must be specified.');
        }

        $quotedSeparators = preg_quote($separators, '/');

        preg_match_all('
            /
                (?!\s)
                    (?:
                        # quoted-string
                        "(?:[^"\\\\]|\\\\.)*(?:"|\\\\|$)
                    |
                        # token
                        [^"'.$quotedSeparators.']+
                    )+
                (?<!\s)
            |
                # separator
                \s*
                (?<separator>['.$quotedSeparators.'])
                \s*

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