How to fix the NullReferenceException error when accessing a variable from another script?

Question

Unity

I make 2 hostile creatures, one attacker, the other scout.
When the scout sees the player, it increases the variable by 1, and the attacker, if this variable becomes greater than 0, starts walking towards the player. But when I access this variable, I get a NullReferenceException error.

if (GetComponent<AI_DronRazved>().call >= 1 )
        {
            angry = true;
            chill = false;
            goBack = false;
        }

Answer 1

How to fix "missing value" error, well I don't even know, can ensure the value exists before it is accessed.