Column conditional format with Json to display attention colour if column is blank

Thanks for this -- I needed to highlight any empty column values in bright red.  I modified your JSON to this: 

{
  "$schema": "http://columnformatting.sharepointpnp.com/columnFormattingSchema.json",
  "elmType": "div",
  "txtContent": "@currentField",
     "style": {
      "background-color": {
         "operator": "?",
         "operands": [
            {
               "operator": "==",
               "operands": [
                 "@currentField", ""
                  ]
            },
            "#FF0000",
            ""
         ]
      }
   }
}

And it works perfectly for what I need!