default vaue in map destructuring can override falsy key values

[ikappaki]

Hi,

t appears there is a bug in map destructuring where an :or default value overrides a key in the destructured map when the key's value is falsy, such as nil.

The expected behavior is that no destructured key should be overridden by an :or default when the key exists, even if its value is falsy.

To reproduce,
Open up the REPL and destructure a map where a key is associated with a nil value while providing a default value of 5. The destructured value is incorrectly set to the default 5 instead of nil

basilisp.user=> (let [{:keys [abc]
                       :or {abc 5}}  {:abc nil}]
                 abc)
5

In contast, Clojure returns nil as expected

user=> (let [{:keys [abc]
              :or {abc 5}}  {:abc nil}]
        abc)
nil

Thanks