Write a function most_common_space_item(items) that receives a list of strings representing names of space objects (e.g., planets, moons). It should count how many times each name appears, then return the name that occurs most often. If the list is empty, return None. If several names share the highest count, return the one that appears first in the input list.
most_common_space_item(["Mars","Venus","Mars","Jupiter"]) # returns "Mars"
most_common_space_item([]) # returns None