Turn off missing frames script

I import sequences to work with. But for coming and testing  i usually import a set of frames from the sequence. So if my c4d sequence is 1-100. Id render only 1,25,50,75,100. Then in AE i import it as a sequence. Those missing frames i would like to have 0% opacity. Cause ill comp as the longer render is running, then i just reimport the sequence. 

Is there an expression i can apply to the opacity? Something like:
if (thisFrame == doesnt exist || thisFrame == All black){
0;
}else{

100:

}

This would be a good help for my method of working.