Merge pull request #3300 from gzzhanghao/gen-fix

Fix generators with default args

packages/babel-plugin-transform-regenerator/test/fixtures/class-argument-scope/example/exec.js

@@ -0,0 +1,8 @@
+class Test {
+  *iter(arg = this) {
+    yield arg;
+  }
+}
+
+let test = new Test;
+assert.equal(test.iter().next().value, test);

packages/babel-plugin-transform-regenerator/test/fixtures/class-argument-scope/options.json

@@ -0,0 +1,5 @@
+{
+  "presets": [
+    "es2015"
+  ]
+}

packages/babel-traverse/src/context.js

@@ -105,6 +105,9 @@ export default class TraversalContext {
       path.resync();
       path.pushContext(this);
 
+      // this path no longer belongs to the tree
+      if (path.key === null) continue;
+
       if (testing && queue.length >= 1000) {
         this.trap = true;
       }