This was intended as a meme but is actually a good representation of what "Null" is. In C#, when you declare string s = "My shit"; it means that "s" is a reference to a memory location that holds the data "My shit". string s = null; means that the reference "s" exists but it's not pointing to any object, as in it holds nothing. More on reddit.com

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This article seems to be a true and correct description of the facts and circumstances surrounding these matters. More on reddit.com

Essentially, the whole command is telling the computer not to take notice of an error and to dump any error messages rather than clutter up the screen or a log file. When you run a unix command, it will either be successful, in which case the output is sent into pipe#1 (which normally points to the monitor screen), or it will fail with an error message which is sent into pipe#2 (which might empty into an error log file or the monitor). The ">" is a command that can redirect those output pipes. In this case it is being told to redirect pipe#2 (the error pipe) to a special unix software device called /dev/null which is basically an infinitely deep hole down which you can throw output that no one cares about seeing. More on reddit.com