Nyholm / psr7

        if (!\is_array($values)) {

            // This is simple, just one value.

            if ((!is_numeric($values) && !\is_string($values)) || 1 !== preg_match("@^[ \t\x21-\x7E\x80-\xFF]*$@", (string) $values)) {

                throw new \InvalidArgumentException('Header values must be RFC 7230 compatible strings.');

            }

            return [trim((string) $values, " \t")];

        }

        // Assert Non empty array

        $returnValues = [];

        foreach ($values as $v) {

            if ((!is_numeric($v) && !\is_string($v)) || 1 !== preg_match("@^[ \t\x21-\x7E\x80-\xFF]*$@", (string) $v)) {

                throw new \InvalidArgumentException('Header values must be RFC 7230 compatible strings.');

            }

            $returnValues[] = trim((string) $v, " \t");

        }