code: def nat_bar_spec():
      return json.loads(
          r"""
  {
    "$schema": "https://vega.github.io/schema/vega/v5.json",
    "background": "white",
    "padding": 5,
    "width": 200,
    "height": 200,
    "style": "cell",
    "data": [
      {
        "name": "dataframe",
        "url": "vegafusion+dataset://dataframe",
        "format": {"type": "json", "parse": {"NULL_TEST": "date"}},
        "transform": [
          {
            "type": "stack",
            "groupby": ["NULL_TEST"],
            "field": "SALES",
            "sort": {"field": [], "order": []},
            "as": ["SALES_start", "SALES_end"],
            "offset": "zero"
          },
          {
            "type": "filter",
            "expr": "(isDate(datum[\"NULL_TEST\"]) || (isValid(datum[\"NULL_TEST\"]) && isFinite(+datum[\"NULL_TEST\"]))) && isValid(datum[\"SALES\"]) && isFinite(+datum[\"SALES\"])"
          }
        ]
      }
    ],
    "marks": [
      {
        "name": "layer_0_marks",
        "type": "rect",
        "clip": true,
        "style": ["bar"],
        "from": {"data": "dataframe"},
        "encode": {
          "update": {
            "tooltip": {
              "signal": "{\"NULL_TEST\": timeFormat(datum[\"NULL_TEST\"], '%b %d, %Y'), \"SALES\": format(datum[\"SALES\"], \"\")}"
            },
            "fill": {"value": "#4c78a8"},
            "ariaRoleDescription": {"value": "bar"},
            "description": {
              "signal": "\"NULL_TEST: \" + (timeFormat(datum[\"NULL_TEST\"], '%b %d, %Y')) + \"; SALES: \" + (format(datum[\"SALES\"], \"\"))"
            },
            "xc": {"scale": "x", "field": "NULL_TEST"},
            "width": {"value": 5},
            "y": {"scale": "y", "field": "SALES_end"},
            "y2": {"scale": "y", "field": "SALES_start"}
          }
        }
      }
    ],
    "scales": [
      {
        "name": "x",
        "type": "time",
        "domain": {"data": "dataframe", "field": "NULL_TEST"},
        "range": [0, {"signal": "width"}],
        "padding": 5
      },
      {
        "name": "y",
        "type": "linear",
        "domain": {"data": "dataframe", "fields": ["SALES_start", "SALES_end"]},
        "range": [{"signal": "height"}, 0],
        "nice": true,
        "zero": true
      }
    ],
    "axes": [
      {
        "scale": "x",
        "orient": "bottom",
        "gridScale": "y",
        "grid": true,
        "tickCount": {"signal": "ceil(width/40)"},
        "domain": false,
        "labels": false,
        "aria": false,
        "maxExtent": 0,
        "minExtent": 0,
        "ticks": false,
        "zindex": 0
      },
      {
        "scale": "y",
        "orient": "left",
        "gridScale": "x",
        "grid": true,
        "tickCount": {"signal": "ceil(height/40)"},
        "domain": false,
        "labels": false,
        "aria": false,
        "maxExtent": 0,
        "minExtent": 0,
        "ticks": false,
        "zindex": 0
      },
      {
        "scale": "x",
        "orient": "bottom",
        "grid": false,
        "title": "NULL_TEST",
        "labelFlush": true,
        "labelOverlap": true,
        "tickCount": {"signal": "ceil(width/40)"},
        "zindex": 0
      },
      {
        "scale": "y",
        "orient": "left",
        "grid": false,
        "title": "SALES",
        "labelOverlap": true,
        "tickCount": {"signal": "ceil(height/40)"},
        "zindex": 0
      }
    ],
    "config": {
      "range": {"ramp": {"scheme": "yellowgreenblue"}},
      "axis": {"domain": false}
    }
  }
      """
      )
  
imports: import pandas
  import pytest
  from pandas import Timestamp, NaT
  import pyarrow
  import vegafusion
  import json
  import polars
  from datetime import date
  import decimal
  import base64
label_desc: Use image node_id 8 for calling a global function with example usage: nat_bar_spec() and returns: json