Implemented transform-void-to-nothing plugin.

Removes the 'void 0' rval for let-/var-assignments.

packages/babel-plugin-transform-void-to-nothing/.npmignore

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+src
+__tests__
+node_modules
+*.log

packages/babel-plugin-transform-void-to-nothing/README.md

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+# babel-plugin-transform-void-to-nothing
+
+This changes 'void 0' rval in var-/let-assignments to nothing.
+
+## Example
+
+**In**
+
+```javascript
+var a = void 0;
+let b = void 0;
+const c = void 0;
+```
+
+**Out**
+
+```javascript
+var a;
+let b;
+const c = void 0;
+```
+
+## Installation
+
+```sh
+$ npm install babel-plugin-transform-void-to-nothing
+```
+
+## Usage
+
+### Via `.babelrc` (Recommended)
+
+**.babelrc**
+
+```json
+{
+  "plugins": ["babel-plugin-transform-void-to-nothing"]
+}
+```
+
+### Via CLI
+
+```sh
+$ babel --plugins babel-plugin-transform-void-to-nothing script.js
+```
+
+### Via Node API
+
+```javascript
+require("babel-core").transform("code", {
+  plugins: ["babel-plugin-transform-void-to-nothing"]
+});
+```

packages/babel-plugin-transform-void-to-nothing/__tests__/babel-plugin-transform-void-to-nothing-test.js

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+jest.autoMockOff();
+
+const babel = require("babel-core");
+const plugin = require("../src/index");
+
+function transform(code) {
+  return babel.transform(code,  {
+    plugins: [plugin],
+  }).code;
+}
+
+describe("transform-void-to-nothing-plugin", () => {
+  it("should transform `void 0` var-assignments to nothing", () => {
+    const source = "var x = void 0;";
+    const expected = "var x;";
+    expect(transform(source)).toBe(expected);
+  });
+
+  it("should transform multiple `void 0` assignments to nothing", () => {
+    const source = "var a = void 0, b = 3, c = void 0, d;";
+    const expected = "var a,\n    b = 3,\n    c,\n    d;";
+    expect(transform(source)).toBe(expected);
+  });
+
+  it("should transform `void 0` let-assignments to nothing", () => {
+    const source = "let a = void 0;";
+    const expected = "let a;";
+    expect(transform(source)).toBe(expected);
+  });
+
+  it("should not transform `void 0` const-assignments", () => {
+    const source = "const a = void 0;";
+    const expected = source;
+    expect(transform(source)).toBe(expected);
+  });
+});

packages/babel-plugin-transform-void-to-nothing/src/index.js

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+"use strict";
+
+const v0 = require("../../babel-helper-is-void-0/src");
+
+module.exports = function({ types: t }) {
+  // "var a = void 0;" -> "var a;"
+  const isVoid0 = v0(t);
+  return {
+    name: "transform-void-to-nothing",
+    visitor: {
+      VariableDeclaration({node: {kind: kind, declarations: declarations}}) {
+        if (kind !== "const") {
+          for (const declaration of declarations) {
+            if (isVoid0(declaration.init)) {
+              declaration.init = null;
+            }
+          }
+        }
+      }
+    },
+  };
+};