Parsing nix-env's performance statistics failed.

Parse error:
Error("expected ident", line: 1, column: 3)

Evaluation output:
trace: { argv = <CODE>; displayName = <CODE>; language = <CODE>; logo32 = <CODE>; logo64 = <CODE>; }
trace: { argv = <CODE>; displayName = <CODE>; language = <CODE>; logo32 = <CODE>; logo64 = <CODE>; }
trace: { argv = <CODE>; displayName = <CODE>; language = <CODE>; logo32 = <CODE>; logo64 = <CODE>; }
trace: { argv = <CODE>; displayName = <CODE>; language = <CODE>; logo32 = <CODE>; logo64 = <CODE>; }
trace: { argv = <CODE>; displayName = <CODE>; language = <CODE>; logo32 = <CODE>; logo64 = <CODE>; }
trace: { argv = <CODE>; displayName = <CODE>; language = <CODE>; logo32 = <CODE>; logo64 = <CODE>; }
trace: { argv = <CODE>; displayName = <CODE>; language = <CODE>; logo32 = <CODE>; logo64 = <CODE>; }
trace: { argv = <CODE>; displayName = <CODE>; language = <CODE>; logo32 = <CODE>; logo64 = <CODE>; }
{
  "cpuTime": 213.248,
  "envs": {
    "number": 109904547,
    "elements": 165225393,
    "bytes": 3080275896
  },
  "list": {
    "elements": 200366560,
    "bytes": 1602932480,
    "concats": 7540069
  },
  "values": {
    "number": 232198766,
    "bytes": 5572770384
  },
  "symbols": {
    "number": 356621,
    "bytes": 16187377
  },
  "sets": {
    "number": 28232414,
    "bytes": 8022142624,
    "elements": 324845138
  },
  "sizes": {
    "Env": 16,
    "Value": 24,
    "Bindings": 8,
    "Attr": 24
  },
  "nrOpUpdates": 13306096,
  "nrOpUpdateValuesCopied": 239164521,
  "nrThunks": 159085632,
  "nrAvoided": 154987202,
  "nrLookups": 77491646,
  "nrPrimOpCalls": 67661675,
  "nrFunctionCalls": 95906687,
  "gc": {
    "heapSize": 12264599552,
    "totalBytes": 23789672928
  }
}