Trying a first version.

node_modules/@fastify/busboy/lib/utils/getLimit.js

@@ -0,0 +1,16 @@
+'use strict'
+
+module.exports = function getLimit (limits, name, defaultLimit) {
+  if (
+    !limits ||
+    limits[name] === undefined ||
+    limits[name] === null
+  ) { return defaultLimit }
+
+  if (
+    typeof limits[name] !== 'number' ||
+    isNaN(limits[name])
+  ) { throw new TypeError('Limit ' + name + ' is not a valid number') }
+
+  return limits[name]
+}