Invalid file when adding header row but column type is 'number'

[gozzoo]

const conf = {
    stylesXmlFile: __dirname + '/styles.xml',
    name: 'report-is-a-thing',
    cols: [
      { type: 'string', width: 15 },
      { type: 'string', width: 25 },
      { type: 'number', width: 30 }
    ],
    rows: [
      [ { value: 'First Name', style: 1 }, 
        { value: 'Last Name', style: 1 }, 
        { value: 'Age', style: 1 } ],
      ['Bruce', 'Wayne', 20],
      ['Clark', 'Kent', 25],
      ['This cell is going to be merged', '', 30],
      ['Peter', 'Parker', 35]
    ]
  };

Here the type of the third column is number but its header is obviously a string.

I think the problem could be solved if its possible for cell object to have its own type property:

{ value: 'Age', style: 1, type: 'string' }