Is it bad that i don't have 'wet-dreams'?

im 13 and either i have never had a wet dream or im just not sure on what it actully is because is that class where school teachs boys how there bodies are changing or gonna change, they say a wet-dream is when you **** in your pants while you dream i guess. is that it? Because if it is thats what it is, thats never happened to me? should i be worried? or is it because i masterbait atleast once or 2 times a-day? and i do that because masterbaiting will give you a bigger penis right?