{
    "expression": ["index-of", ["get", "substr"], ["get", "str"]],
    "inputs": [
      [{}, {"properties": {"substr": null, "str": "helloworld"}}],
      [{}, {"properties": {"substr": "foo", "str": "helloworld"}}],
      [{}, {"properties": {"substr": "low", "str": "helloworld"}}],
      [{}, {"properties": {"substr": true, "str": "falsetrue"}}],
      [{}, {"properties": {"substr": false, "str": "falsetrue"}}],
      [{}, {"properties": {"substr": 123, "str": "hello123world"}}],
      [{}, {"properties": {"substr": "low", "str": null}}]
    ],
    "expected": {
      "compiled": {
        "result": "success",
        "isFeatureConstant": false,
        "isZoomConstant": true,
        "type": "number"
      },
      "serialized": ["index-of", ["get", "substr"], ["get", "str"]],
      "outputs": [
        -1,
        -1,
        3,
        5,
        0,
        5,
        {
          "error": "Expected second argument to be of type array or string, but found null instead."
        }
      ]
    }
  }