how can i past only in Blank cell not all of Cell

this script is writing all cell in C to same Value as B but i just need to Write only Blank Cell with the value of B.

can some one find the error in this funktion????

function fill() {
  var tss = SpreadsheetApp.getActiveSpreadsheet();
  var values = tss.getRange("data!C:C").getValues();

  for(i=0; i<values.length; i++) {
    var value = values[i][0];

    if (value == "") {

      var rangeA = tss.getSheetByName("data").getRange(i+1,2);
      var rangeB = tss.getSheetByName("data").getRange(i+1,3);
      var copypaste = tss.getSheetByName("data");

      if(!rangeA.isBlank()) {
        copypaste.getRange("B2:B").copyTo(copypaste.getRange("C2:C"),{contentsOnly:true})
      }
    }
  }
}