Nested object returns as null if first property is null

Given the query
`const query = knex.select(['table.col_a AS _nested_colA','table.col_b AS _nested_colB']);`

am I right to assume that with `table.col_a` as `null` and `table.col_b` as `foo` I should be getting back
```
{
  nested: {
    colA: null,
    colB: 'foo'
  }
}
```

However, I get 
```
{
  nested: null
}
```

Is this how it should be working or might this be a bug?