问如何访问嵌套数组的最后一个索引

EN

{

"result": {
    "86400": [
      [
        1381190400,
        123.610000,
        123.610000,
        123.610000,
        123.610000,
        0.100000,
        0.0
      ],
      [
        1381276800,
        123.610000,
        124.190000,
        123.900000,
        124.180000,
        3.991600,
        0.0
      ],
     ...

      [
        1600646400,
        11078,
        11078,
        10906.9,
        10950.4,
        623.00835437,
        6841501.73480653
      ]
    ]
  },

"allowance": {
    "cost": 0.015,
    "remaining": 9.985,
    "upgrade": "For unlimited API access, create an account at ________"
  }
}

 [
        1600646400,
        11078,
        11078,
        10906.9,
        10950.4,
        623.00835437,
        6841501.73480653
      ]

http.Response historicalResponse = await http.get(historicalRequestURL);

var decodedHistorical = jsonDecode(historicalResponse.body);

var historicalPrice = decodedHistorical['result']['86400'.length - 1][0];

print(historicalPrice);

"NoSuchMethodError: The method '[]' was called on null."
"Receiver: null"
"Tried calling: [](0)"

var historicalPrice = decodedHistorical['result']['86400'][decodedHistorical.length - 1][0];