Take host API for example and method get().
Create a request:

{
    "output": [
        "name"
    ],
    "hostids": [
        "10511", "10512"
    ],
    "sortfield": "name",
    "countOutput": true
}

No result is given, but in logs we can see the error:

Query failed: ERROR: column "h.name" must appear in the GROUP BY clause or be used in an aggregate function
This is bad.