lunr.js: Uncaught TypeError: Cannot read property 'tf' of undefined

Hello, I am getting this error “Uncaught TypeError: Cannot read property ‘tf’ of undefined” in 0.7.2. (I was getting it in 0.5 as well, so upgraded, still getting it.)

It does not fail for every search; just some. I can’t figure out how to debug this or identify what is different between the search terms that work and the ones that don’t.

Note: I have a web site created by an now unavailable developer. I am hacking my way through trying to fix problems like this. I know just enough JS, etc, to be dangerous, but not enough to know what I am doing.

My browser reports the error on the tf = line here:

lunr.Index.prototype.documentVector = function (documentRef) {
  var documentTokens = this.documentStore.get(documentRef),
      documentTokensLength = documentTokens.length,
      documentVector = new lunr.Vector

  for (var i = 0; i < documentTokensLength; i++) {
    var token = documentTokens.elements[i],
        tf = this.tokenStore.get(token)[documentRef].tf,
        idf = this.idf(token)

    documentVector.insert(this.corpusTokens.indexOf(token), tf * idf)
  };

  return documentVector
}

It seems to be a something to do with this function. When I get the error, this function bails out at the if statement.

lunr.TokenStore.prototype.getNode = function (token) {
  if (!token) return {}

  var node = this.root

  for (var i = 0; i < token.length; i++) {
    if (!node[token.charAt(i)]) return {}

    node = node[token.charAt(i)]
  }

  return node
}

Any suggestions how I can debug this or fix it? Thank you. – Mike