我该如何修复这个错误:
Cannot call method 'Kc' of null in Google graph
JSON:
{
"cols": [{
"label": "name",
"type": "string"
}, {
"label": "id",
"type": "int"
}, {
"label": "quiz_id",
"type": "int"
}, {
"label": "score",
"type": "int"
}],
"rows": [{
"c": [{
"v": "kumar"
}, {
"v": "40"
}, {
"v": "46"
}, {
"v": "46"
}]
}, {
"c": [{
"v": "kumar"
}, {
"v": "36"
}, {
"v": "46"
}, {
"v": "46"
}]
}, {
"c": [{
"v": "kumar"
}, {
"v": "35"
}, {
"v": "46"
}, {
"v": "46"
}]
}, {
"c": [{
"v": "kumar"
}, {
"v": "10"
}, {
"v": "46"
}, {
"v": "46"
}]
}]
}