Null refrence error when attepting to addChild

programming flash
1

I am attempting to make a class that handles the building in a game, but I can’t get the object to come on stage. I can get everything to work if I am on the timeline, just not from this class.

I’ve been getting this:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at build$/newBuild()[/Users/student/Desktop/attack/build.as:19]

I attempted to see if my building variable was null so i did a trace…

trace (building);
and got:
[object base]


package {


 import flash.display.Sprite;
 import flash.display.Stage;
 import base; 
 
 public class build {
    
    public static var theStage:Stage;
    
     public static function newBuild():void
      {
        
        var building:base = new base();
        trace(building);
        building.x = 250;
        building.y = 250;
        theStage.addChild(building);

      }
   }
}

This class is being called from the timeline with:

build.newBuild();

Thanks for any help! =]