minor pr changes

Author: FelixVaughan

lib/core/util.js

@@ -905,14 +905,14 @@ Object.setPrototypeOf(normalizedMethodRecordsBase, null)
 Object.setPrototypeOf(normalizedMethodRecords, null)
 
 /**
- * @param {Record<string, string | string[]> | Iterable<[string, string]> | string[]}
+ * @param {Record<string, string | string[]> | Iterable<[string, string]> | string[]} opts
  * @returns {Record<string, string[] | string>}
  */
 function normalizeHeaders (opts) {
   const headers = {}
   const src = opts.headers
 
-  if (src == null) return headers
+  if (typeof src !== 'object' || src === null) return headers
 
   if (Array.isArray(src)) {
     for (let i = 0; i < src.length; i += 2) {
@@ -934,12 +934,10 @@ function normalizeHeaders (opts) {
     return headers
   }
 
-  if (typeof src === 'object') {
-    for (const key of Object.keys(src)) headers[key.toLowerCase()] = src[key]
-    return headers
+  for (const key of Object.keys(src)) {
+    headers[key.toLowerCase()] = src[key]
   }
-
-  throw new InvalidArgumentError('opts.headers is not an object')
+  return headers
 }
 
 module.exports = {