fix: type error by xmldom

[KazuCocoa]

lib/defaults-utils.js:15:14 - error TS2304: Cannot find name 'Node'.

15  * @returns {Node|string} Either string or raw node representation of
                ~~~~

lib/defaults-utils.js:28:7 - error TS18047: 'xmlDoc.documentElement' is possibly 'null'.

28       xmlDoc.documentElement.appendChild(keyEl);
         ~~~~~~~~~~~~~~~~~~~~~~

lib/defaults-utils.js:31:7 - error TS18047: 'xmlDoc.documentElement' is possibly 'null'.

31       xmlDoc.documentElement.appendChild(subValueEl);
         ~~~~~~~~~~~~~~~~~~~~~~

lib/defaults-utils.js:38:7 - error TS18047: 'xmlDoc.documentElement' is possibly 'null'.

38       xmlDoc.documentElement.appendChild(subValueEl);
         ~~~~~~~~~~~~~~~~~~~~~~

lib/defaults-utils.js:49:5 - error TS18047: 'xmlDoc.documentElement' is possibly 'null'.

49     xmlDoc.documentElement.appendChild(valueTextEl);
       ~~~~~~~~~~~~~~~~~~~~~~

lib/defaults-utils.js:58:45 - error TS2345: Argument of type 'Element | null' is not assignable to parameter of type 'Node'.
  Type 'null' is not assignable to type 'Node'.

58     ? new XMLSerializer().serializeToString(xmlDoc.documentElement)
                                               ~~~~~~~~~~~~~~~~~~~~~~


Found 6 errors.

[github-actions]

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