Sunday's at Tiffany's by James Patterson and Gabrielle Charbonnet

This book is about a little girl who has an imaginary friend.  On her ninth birthday he has to leave her because kids can't have imaginary friends after they turn nine.  It's the rules.  It's also the rules that she is supposed to forget he ever existed the very next day.  Flash forward 20 something years later.  She didn't forget about him and she's even written a broadway play about it.  Then one day their paths cross which has never ever happened to any imaginary friend.  For some reason they are brought together again and I won't tell you why.  I thought this book was good but not one of my favorites.  One thing had me wondering who wrote the majority of the book, James Patterson or Gabrielle Charbonnet?  James Patterson cranks out quite a few books and sometimes there are coauthors.  It makes me wonder if his name is attached just to sell books.