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

Not a native, but we have the same "problem" in German (I am a software developer, so I often have to use NULL in my work day), so I would like to give my two cents anyway. I pronounce the number just like a normal person would, with German pronounciation. And the NULL value I pronounce with an English pronounciation. For everyone else (ie, everyone who doesn't work in IT) it really doesn't matter. 0 is 0 and they have no concept of what a NULL value might be anyway. More on reddit.com