Sometimes, software issues are too silly and simple!

Hello all, 

I'm writing this post to point at a common mistake that may waste a lot of time as happened to me, Although I'm not beginner, but I had that silly experience.

one of my comps in AE was showing black scren in composition window, sounds are played, new layers are okay, but all other layers not visible!
I checked all layers for opacity, scale and position to make sure it's all correct, then tried a bunch of bug fixes available on Adobe forum for AE, then after no short time, I discovered that it was all about one null layer scaled to "0" with all thoses layers parented to!
Although it seems too silly and funny but I just want to say, double and tripple  check everything before thinking of  bug fixes!