That must be what caused Xur to come to the Tower without any weapons to sell. As he was grabbing three pieces of armor that no one needed, he saw that his Marijuana provider left him a bag of Marijuana under the door. Xur walked over to the bag, picked it up, and walked over to his Marijuana smoking chair. He sat down and promptly began to smoke. After sitting there in a daze for an hour he realizes that it's time to leave for the Tower. Picking up his bag labelled, "Bag o' Trolls," he hops in his ship and heads for the Tower. When Xur arrived at the Tower he realized that he forgot to bring a weapon. He thought to himself, "I am here to troll the Guardians. They won't notice the absence of a weapon from my selection this week."