If you set a default value to the select2 dropdown ($this->val), then ".select2('val', '$this->val')" will be appended to the select2 initiator.
If $this->val is not set (or empty) then the default value will not be set, just normal select2 behavior.

For more information, see the following select2 issue:
https://github.com/ivaynberg/select2/issues/283