Null

null is a reserved constant used in Java and similar programming languages that is used to represent a void reference. In simpler terms, it is a value used to represent that a reference variable has no set value. In RuneScape it usually appears in string values either due to a variable not being assigned in time, usually due to lag, or as the result of a glitch.
It first made its appearance in game as a player name some people would see from time to time in RuneScape Classic. This can occasionally appear when moving between areas like going up and down stairs. This usually occurred when players with dial-up, or similar low speed, internet logged in and tried to type something.
Null items
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An item also can be called "null", meaning the information of the object didn't load. Previously, if one typed in 'null' on the quick chat system, this item could be referred to. This was removed in a hidden update. Another instance of null items occurred when a player sent an item to their bank using the Winter Storage scroll.
In the past if you searched bank item "null" you would get a message stating a number of search results equal to the number of empty spaces in your bank. This is explained by banks being represented as a List of items where empty slots are a null reference and occupied slots are references to the items they hold.
Make null
editPreviously when making items, "null" was displayed for a split second in the "How many would you like to make?" interface. This tended to happen more often while smelting. Null could also be made by dropping an object, right clicking the object again before it is removed from your inventory, clicking "Use" and right clicking on another object.
Logging in
editSometimes, immediately after logging in, if a player talks or the game makes the player say something, the player's name will appear as 'null' in the chat box.
Null scenery
editIn Legacy of Seergaze, players repair a furnace. For a time after the quest was released, players could stand on the story above, and see the furnace through a hole in the floor. They could right-click on the top of the furnace (which registered as non-interactive scenery), and the menu would include the option "Examine null". This was later fixed by Jagex.
Adventurer's log Null
editWhen Livid Farm was released, the Adventurer's log became glitched resulting in all of the entries reading "null". Examples include:"Item Found : Null.", "I killed null null", "I killed null null null null null null in Daemonheim." or other similar sentences. This happened for everyone with sentences containing a boss monster name, item names, or a completed treasure trail. For quest completions, it displayed the title correctly but 'null' appeared after the title. This was fixed the next week on 12 April 2011.
Gallery
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Buying Ingredients for Moonshine from the Grand Exchange
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Null glitch on players adventurers log