@@toStringTag spoofing for null and undefined

[Gary Guo]

Now I have a tendency to support the suggestion that cuts the anti-spoofing part. If coder wants to make an object and pretend it's a built-in, let it be. The anti-spoofing algorithm could not prevent this case:```Object.prototype.toString = function(){  return '[object I_Can_Be_Anything]';}``` 		 	   		  
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