Condition if not general for every command

I searched for if not commands, found a lot of answer for specific commands, but if I want something for any commands, how to do it? I'd like to know if there is a way for every condition to reverse it's result... not like knowing -eq and -ne...

what I want to do is a not of this

while [ -z ${!specificCommands[$d]} ]

I will appreciate the answer specific for this command, but my point is to just reverse like in C with !