Avoid inserting checkbox into empty cells in forEach loop – Google apps script

I have a list of ranges where depending on the cell value, a checked checkbox (Completada) or an unchecked checkbox (No completada) should be inserted.

The problem I have is that the script places checkbox in the entire list of ranges, it does not ignore empty cells or cells that do not contain those specific values.

It’s probably a very slight problem, but I can’t fix it.

This is my actual code:

function checkboxVistaMensual_comparacion() {
  const ss = SpreadsheetApp.getActiveSpreadsheet();
  const targetSheet = ss.getSheetByName('Calendario');  // Hoja Destino

  var rangesCheckbox = targetSheet.getRangeList(['F6:F98', 'I6:I98', 'L6:L98', 'O6:O98', 'R6:R98', 'U6:U98', 'X6:X98']);
  var rangesCheckboxVal = rangesCheckbox.getRanges();
  
  var c = 'Completada';
  var nc = 'No completada';

  var valores = []
  rangesCheckboxVal.forEach((row)=> {

    if ( row.valueType == SpreadsheetApp.ValueType.CHECKBOX ) return;
    if ( row == '' ) return;

    if ( row == c ){
      valores.push(c);
    } else {
      if ( row == nc ){
      valores.push(nc);
      }
    }

  })  

  rangesCheckbox.insertCheckboxes(c, nc);
}