code: function () {
              var placeholder = this.getPlaceholder();
  
              if (this.isPlaceholderOptionSelected() && placeholder !== undefined) {
  
                  // check for a placeholder option if attached to a select
                  if (this.select && this.getPlaceholderOption() === undefined) return;
  
                  this.selection.find(".select2-chosen").html(this.opts.escapeMarkup(placeholder));
  
                  this.selection.addClass("select2-default");
  
                  this.container.removeClass("select2-allowclear");
              }
          }
docs: single