Your pop_byte routine reads as follows:

		char pop_byte(){
			get_byte(nextPos++);
			/*
			char read = get_byte(nextPos++);
			//Serial.print("Popped: '");
			//Serial.write(read);
			//Serial.println("'");
			return read;
			*/
		}

There is no return here.

Normally I would submit a pull request but if you see the other issue I filed (with the name change) then you can imagine that my pull request would look very odd. Pretty simple bug and fix.