hx-vals + json-enc: first-level empty array is dropped

htmx.org 2.0.10, json-enc 2.0.3. This bug breaks some cases of the programmatic population of `hx-vals`. E.g. as in the example from the [docs](https://htmx.org/attributes/hx-vals/): `hx-vals='js:{...foo()}'` where `foo()` returns a map where some first-level value is `[]`. ` ## Steps See https://jsfiddle.net/r4sgw3nh: ```html <script src="https://unpkg.com/htmx.org@2.0.10"></script> <script src="https://unpkg.com/htmx-ext-json-enc@2.0.3/json-enc.js"></script> <button type="button" hx-ext="json-enc" hx-post="/test" hx-vals='js:{ "firstLevel": [], "secondLevel": { "values": [] } }'> Click me </button> ``` 1) Click `Click me`. 2) Inspect the made request payload in the browser devtools. # Actual `{"secondLevel":{"values":[]}}` # Expected `{"firstLevel":[],"secondLevel":{"values":[]}}`