input: Write a python function to check if a book is fiction based on its genre using JSON data.
  assert check_if_fiction('{"title": "The Catcher in the Rye", "author": "JD Salinger", "genre": "Novel"}') == "Book is fiction"
  assert check_if_fiction('{"title": "A Brief History of Time", "author": "Stephen Hawking", "genre": "Science"}') == "Book is not fiction"
  assert check_if_fiction('{"title": "To Kill a Mockingbird", "author": "Harper Lee", "genre": "Novel"}') == "Book is fiction"
output: import json
  
  def check_if_fiction(book_json):
      book = json.loads(book_json)
      fiction_genres = ["Novel", "Fiction", "Fantasy", "Science Fiction", "Mystery", "Thriller", "Horror"]
      if book["genre"] in fiction_genres:
          return "Book is fiction"
      else:
          return "Book is not fiction"