How to debug: SIGBUS: Illegal storage access. (Attempt to read from nil?)

[gcao]

I have below code that is throwing "SIGBUS: Illegal storage access. (Attempt to 
read from nil?)" at line 4, even though all arguments are not nil. If it's 
thrown from evaluator proc, should the stack be showing the line inside 
evaluator instead?
    
    
    echo self == nil # false
    echo frame == nil # false
    echo expr.evaluator == nil # false
    expr.evaluator(self, frame, expr)
    
    
    Run