Grabbed dndbeyond's source code

```
~/go/bin/sourcemapper -output ddb -jsurl https://media.dndbeyond.com/character-app/static/js/main.90aa78c5.js
```

ddb_main/node_modules/@mui/system/esm/merge.js

@@ -0,0 +1,10 @@
+import deepmerge from '@mui/utils/deepmerge';
+function merge(acc, item) {
+  if (!item) {
+    return acc;
+  }
+  return deepmerge(acc, item, {
+    clone: false // No need to clone deep, it's way faster.
+  });
+}
+export default merge;