Create a zero value of a generic Number subclass

Zero isn't even mentioned in the Number class. If you must do this, and I suggest avoiding nulls, is perhaps:

public static <T> T coalesce(T a, T b) {
    return a==null ? b : a;
}

You could also create a generic interface for handling numbers with features that make sense to your code:

interface NumberOps<T extends Number> {
    T zeroIfNull(T value);
}

Is it possible to do this at all?
Not really. For one thing, when value is null, how would method know which Number implementation to return?

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