Issue with using a validation function for trailing/leading whitespaces in Sanity.io

validation: (Rule) => Rule.required().custom((blocks) => {
   const offendingPaths = (blocks || [])
      .filter(({ _type, children }) => {
         if (_type !== "block") return false;

         const { 0: first, length, [length - 1]: last } = children || [];

         return first?.text.startsWith(" ") || last?.text.endsWith(" ")
      })
      .map((block, index) => [{ _key: block._key }] || [index]);
   return (
      offendingPaths.length === 0 || {
         message: "Blocks cannot start or end with whitespace",
         paths: offendingPaths,
      }
   )
}),

export default {
   name: "instructor",
   title: "Instructor",
   type: "document",
   fields: [
      {
         name: "name",
         title: "Name",
         type: "string",
         validation: << rule is here >>,
      },
      {
         name: "bio",
         title: "Bio",
         type: "text",
      },... ]}

validation: Rule => Rule.custom(name => {
  if (name.startsWith(' ') || name.endsWidth(' ')) {
    return 'No trailing space'
  }
  return true
})

    if (typeof name === 'undefined') {
      return false
    }