Suggestion: parameter can be demoted to base class

Hello,

What does this message mean?

Suggestion: parameter can be demoted to base class

I got this message on MonoDevelop on the method OnTriggerExit2D

 void OnTriggerExit2D (Collider2D other)
 {

 }

But it's really weird because I don't see this suggestion on the method OnTriggerEnter2D:

     void OnTriggerEnter2D (Collider2D other)
     {
             if (isDragged)
                     dropZone = other;
     }