Three uses of `hasOwnProperty.call` have been replaced with simpler
alternatives. I did this because I found this convention confusing.
The `ComposableObservableStore` changes required adding a check for
whether the `config` is defined, because the old syntax would allow
iterating over `undefined` as if it was an empty object. Functionally
it should be identical. A new test was added to highlight this
functionality.
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