Something nugatory has no real value; it’s worthless. All your excuses for why you didn’t turn the bath tap off when you left the apartment are nugatory; they don’t change the fact that the tub overflowed and leaked into the apartment below.
An adjective meaning “trifling, of no value,” nugatory comes from the Latin nugatorius “worthless, futile,” which in turn came from the also Latin nugatory — “jester, trifle.” It’s a word you probably don’t hear too often, but it’s a fun and descriptive one to use. Describe something with no force or importance as nugatory. "Whether this rug is red or green is nugatory to someone who is colorblind."