(decedent was art collector that gifted art collection to family members via interests in LLC but died within three years of the gifts; gifts were of LLC units not exceeding the decedent's "basic exclusion amount" plus annual exclusion gifts with any remaining value transferred in LLC units in a later year; appraisal of artwork cam in higher than expected and assignment of LLC interests amended in later year to provide that family members would pay any resulting gift tax; upon death, surviving spouse seeks to have gifts canceled or that family members pay estate and gift tax based on actual value of gifted property if they retain gifts; court interpreted 2001 and 2002 gift documents as decedent's desire to give LLC units free of any obligation of donees to pay gift tax; blank spaces in assignment simply ministerial act of completing parties' original agreement).