Fix type to allow explicit null, etc

Author: wooorm

lib/index.js

@@ -148,16 +148,17 @@ const blockOrCaption = convertElement([
  *
  * @param {Nodes} tree
  *   Tree to turn into text.
- * @param {Options} [options]
+ * @param {Readonly<Options> | null | undefined} [options]
  *   Configuration (optional).
  * @returns {string}
  *   Serialized `tree`.
  */
-export function toText(tree, options = {}) {
+export function toText(tree, options) {
+  const options_ = options || {}
   const children = 'children' in tree ? tree.children : []
   const block = blockOrCaption(tree)
   const whitespace = inferWhitespace(tree, {
-    whitespace: options.whitespace || 'normal',
+    whitespace: options_.whitespace || 'normal',
     breakBefore: false,
     breakAfter: false
   })