Flow doesn't that map.has means that I can use map.get

packages/babel-preset-env/src/index.js

@@ -161,8 +161,8 @@ const removeUnnecessaryItems = (
   overlapping: Map<string, Set<string>>,
 ) => {
   items.forEach(item => {
-    if (!overlapping.has(item)) return;
-    overlapping.get(item).forEach(name => items.delete(name));
+    const names = overlapping.get(item);
+    if (names) names.forEach(name => items.delete(name));
   });
 };