Why does IsCoinBase() check if there is exactly one input?

In the Bitcoin Core source code there is a function to check if a given transaction is a coinbase or not:

 bool IsCoinBase() const { return (vin.size() == 1 && vin[0].prevout.IsNull()); }

Does it really need to check if vin.size() is equal to 1? Isn't vin[0].prevout.IsNull() a sufficient condition for a transaction to be a coinbase? Is there any situation that the later condition is true but we have more than one input?

The only reason I can guess is to avoid run-time error when vin is empty (so there is no vin[0]).

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