Camera.main, Camera.allCameras, IndexOutOfBound exception

I was developing a game when a wild error appears. I have the next Hierarchy in my scene:

As you can see, my camera has the tag "MainCamera" that i need to access to it with Camera.main. And i access to it with the next code:

 Camera camera = (UseFirstCamera) ? Camera.main : Camera.allCameras[1];

The problem is, with that code i obtain a IndexOutOfBound and I need to use the next code to access the camera:

 Camera camera;
 
 if(Camera.allCamerasCount == 1)
     camera = (UseFirstCamera) ? Camera.main : Camera.allCameras[0];
 else
     camera = (UseFirstCamera) ? Camera.main : Camera.allCameras[1];

Cause the Camera.main is null, but it shouldn't be so i think. am I doing or interpreting something wrong with Camera.main variable? (I need to use Camera.allCameras[] cause in other scenes i have more than one camera).