Following T138104 empty "containers" in the JSON representation of entity data (e.g. returned by wbgetentities API) should be empty JSON objects, not empty JSON array (i.e. `{}` not `[]`}.
It seems statements in forms be still represented as empty JSON arrays in place of empty JSON objects.
For instance, https://www.wikidata.org/w/api.php?action=wbgetentities&format=json&ids=L3872 returns `"claims":[]` in the serialization of `L3872-F2`.
```
{
"entities": {
"L3872": {
(...)
"claims": {},
"forms": [
{
"id": "L3872-F1",
(...)
"claims": []
},
{
"id": "L3872-F2",
(...)
"claims": []
}
],
"senses": [
(...)
]
}
},
"success": 1
}
```
**Expected state (acceptance criterion):**
* if the lexeme form or sense has not statements stored, the JSON representation of its data should contain `claims: {}` entry, not `claims: []`.
**Notes:**
* The patches fixing this issue should already be done by @Lucas_Werkmeister_WMDE and now only need review:
* [ ] https://gerrit.wikimedia.org/r/677353 (WikibaseLexeme, disabling a test)
* [ ] https://gerrit.wikimedia.org/r/676820 (Wikibase, fixing the thing)
* [ ] https://gerrit.wikimedia.org/r/677353 (WikibaseLexeme, reenabling the test from above and adding a new one for the changed functionality)