in table 3.12 1st row - key has null value and mapping function returns null - merge function will associate new value with that key (mapping function isn't even called), won't remove it. Right?
Thanks for reporting this. You are correct. Have a cow for reporting something detailed that was an incorrect fact and not just a typo! (We still like to hear about typos, but incorrect facts are more important!) I've added this to the errata