🐛 Bug Report

Typescript error when using Worksheet.getColumn().eachCell - TS2722: Cannot invoke an object which is possibly 'undefined'.

Lib version: 3.8.0

Steps To Reproduce

Code example

const wb = new ExcelJS.Workbook();
const ws = wb.addWorksheet('XYZ');
...
ws.getColumn(1).eachCell((cell, rowNum) => {
  cell.fill = headerFill;
});

The expected behaviour:

There should be no error.

Possible solution (optional, but very helpful):

Is it possible to clearly define the functions and properties that are available from getColumn?