debug_traceBlockByNumber error with "latest" parameter

[Mummyhap]

The request consistently returns the error 'block #-1 not found.' I believe this is due to a parsing error of the 'latest' parameter in this method.
request:

{
    "method": "debug_traceBlockByNumber",
    "params": [
        "latest",
        {
            "tracer": "callTracer"
        }
    ],
    "id": 1,
    "jsonrpc": "2.0"
}

response:

{
    "jsonrpc": "2.0",
    "id": 1,
    "error": {
        "code": -32000,
        "message": "block #-1 not found"
    }
}