I am working on a script with C# and whenever I run my game, console pops up and says "Object reference not set to an instance of an object. Then when I click it to try and solve the problem, it brings me to this point in my script and I can't figure out what to do...

//Add spheres that can be collided against 
        GameObject[] sp2 = GameObject.FindGameObjectsWithTag ("Softbody");  
        Object[] objs = GameObject.FindObjectsOfType(typeof(GameObject)); 
        allSpheres = new ArrayList(); 
        int cnt=0; 
        for(int i=0;i<sp2.Length;i++) { 
            allSpheres.Add(sp2[i]); 
            cnt++; 
        } 
        for(int i=0;i<objs.Length;i++) 
        {          
            if(objs[i].name == "SphereSoft") {    
                allSpheres.Add(objs[i]); 
                cnt++; 
            } 

        }

Could someone help me out? I will be continuously trying to find my answer on the Unity website.