bone of contention vs undecided

bone of contention

noun
  • Something that continues to be disputed; something on which no agreement can be reached 

undecided

noun
  • A voter etc. who has not yet come to a decision. 

adj
  • Uncommitted, not having reached a decision. 

  • Open and not yet settled or determined. 

How often have the words bone of contention and undecided occurred in a corpus of books? (source: Google Ngram Viewer )