double?.Should().BeApproximately is looking for a float?

I am using 5.4.2 and trying to work with both double and double? type data elements

```
double? d1 = 1.0123;
double expected = 1.01;

d1.Should().BeApproximately(expected, 1.0); <-- this extension doesn't exist
d1.Value.Should().BeApproximately(expected, 1.0) <-- complains that "expected" should be float
```

Shouldn't both work?