Displaying Null or Undefined in React and JavaScript

I wanted to display the undefined or null values as italicize. If its empty string then output as is. If it has a value then output as is.

The problem right now is that its outputting as [Object Object] for null or undefined.

Codesandbox: CODESANDBOX

const columns: GridColDef[] = [
  { field: "id", hide: true },
  {
    field: "col1",
    headerName: "Column 1",
    width: 150,
    renderCell({ value }) {
      return `${
        value === null || value === undefined ? (
          <div style={{ fontStyle: "italic" }}>null</div>
        ) : (
          String(value)
        )
      }`;
    }
  },
  {
    field: "col2",
    headerName: "Column 2",
    width: 150,
    renderCell({ value }) {
      return `${
        value === null || value === undefined ? (
          <div style={{ fontStyle: "italic" }}>null</div>
        ) : (
          String(value)
        )
      }`;
    }
  }
];