Error in custom validation rule for schema in Slack thread

{
      title: "Slug",
      name: "slug",
      type: "slug",
      options: {
        source: "title",
        maxLength: 200, // will be ignored if slugify is set
        slugify: (input: string) => {
          const sanitized = input
            .toLowerCase()
            .replace(/\s+/g, "-")
            .replace(/[^a-zA-Z0-9-]/g, "")
            .slice(0, 200);
          return sanitized;
        },
      },
      validation: (Rule) => [
        Rule.required(),
        Rule.custom((name: string) => {
          if (typeof name === "undefined") {
            return true; // Allow undefined values
          }

          // This would crash if we didn't check
          // for undefined values first
          return name.includes("Brew") ? "you can't use Brew" : true;
        }),
      ],
    },

return name.includes("Brew") ? "you can't use Brew" : true;

interface TypeName {
  _type: 'slug';
  current: string;
}

validation: (Rule) => [
        Rule.required(),
        Rule.custom((name: { _type: string; current: string }) => {
          // This would crash if we didn't check
          // for undefined values first
          if (typeof name === "undefined") {
            return true; // Allow undefined values
          }

          let hasSpecialCharacters = /[^\na-z0-9-]/g.test(name.current);
          return hasSpecialCharacters
            ? "Your slug has characters that are not allowed"
            : true;
        }),
      ],
    },