How to use is-buffer

constructor (seed, hdpath = '') {
  let value = null
  if (typeof seed === 'string') {
   value = Buffer.from(seed)
  } else if (isBuffer(seed)) {
   value = seed
  } else {
   throw new Error('Seed must be Buffer or string')
  }

  this.__hdwallet = hdkey.fromMasterSeed(value)
  this.__hdpath = hdpath
 }

/**
  * Stringify a Unist node representation of a file
  * (in string or VFile representation) into a string
  * using the `Compiler` on the processor.
  *
  * @param {Node} node - Unist node.
  * @param {(string|VFile)?} [file] - File representation.
  * @param {Object?} [options] - Configuration.
  * @return {string} - String representation.
  */
 function stringify(node, file, options) {
  assertConcrete('stringify');
  assertCompiler('stringify');
  assertNode(node);

  if (
   !options &&
   !string(file) &&
   !buffer(file) &&
   !(typeof file === 'object' && 'messages' in file)
  ) {
   options = file;
   file = null;
  }

  return new processor.Compiler(vfile(file), options, processor).compile(node);
 }