diff --git a/src/index.js b/src/index.js
index d4aa5ec..f8335d9 100644
--- a/src/index.js
+++ b/src/index.js
@@ -596,7 +596,8 @@ class TerserPlugin {
             );
           }
 
-          if (output.code) {
+          // Custom functions can return `undefined` or `null`
+          if (typeof output.code !== "undefined" && output.code !== null) {
             let shebang;
 
             if (
diff --git a/test/TerserPlugin.test.js b/test/TerserPlugin.test.js
index 3227f43..be1122f 100644
--- a/test/TerserPlugin.test.js
+++ b/test/TerserPlugin.test.js
@@ -177,6 +177,20 @@ describe("TerserPlugin", () => {
     }
   });
 
+  it("should work with empty files", async () => {
+    const compiler = getCompiler({
+      entry: path.resolve(__dirname, "fixtures/empty.js"),
+    });
+
+    new TerserPlugin().apply(compiler);
+
+    const stats = await compile(compiler);
+
+    expect(readsAssets(compiler, stats)).toMatchSnapshot("assets");
+    expect(getErrors(stats)).toMatchSnapshot("errors");
+    expect(getWarnings(stats)).toMatchSnapshot("warnings");
+  });
+
   it("should work when some of assets do not contain source maps", async () => {
     const compiler = getCompiler({
       devtool: "source-map",
diff --git a/test/__snapshots__/TerserPlugin.test.js.snap b/test/__snapshots__/TerserPlugin.test.js.snap
index 4f20bc0..4316ee9 100644
--- a/test/__snapshots__/TerserPlugin.test.js.snap
+++ b/test/__snapshots__/TerserPlugin.test.js.snap
@@ -1739,6 +1739,16 @@ exports[`TerserPlugin should work with child compilation: errors 1`] = `Array []
 
 exports[`TerserPlugin should work with child compilation: warnings 1`] = `Array []`;
 
+exports[`TerserPlugin should work with empty files: assets 1`] = `
+Object {
+  "main.js": "",
+}
+`;
+
+exports[`TerserPlugin should work with empty files: errors 1`] = `Array []`;
+
+exports[`TerserPlugin should work with empty files: warnings 1`] = `Array []`;
+
 exports[`TerserPlugin should work with multi compiler mode with source maps: assets 1`] = `
 Object {
   "main-1.js": "(()=>{var __webpack_modules__={921:module=>{eval(\\"{// foo\\\\n/* @preserve*/\\\\n// bar\\\\nconst a = (/* unused pure expression or super */ null && (2 + 2));\\\\n\\\\nmodule.exports = function Foo() {\\\\n  const b = 2 + 2;\\\\n  console.log(b + 1 + 2);\\\\n};\\\\n\\\\n\\\\n//# sourceURL=webpack://terser-webpack-plugin/./test/fixtures/entry.js?\\\\n}\\")}},__webpack_module_cache__={};function __webpack_require__(e){var _=__webpack_module_cache__[e];if(void 0!==_)return _.exports;var r=__webpack_module_cache__[e]={exports:{}};return __webpack_modules__[e](r,r.exports,__webpack_require__),r.exports}var __webpack_exports__=__webpack_require__(921)})();",
@@ -3377,14 +3387,8 @@ exports[`TerserPlugin should work, extract comments in one file and use memory c
 
 exports[`TerserPlugin should write stdout and stderr of workers to stdout and stderr of main process in not parallel mode: assets 1`] = `
 Object {
-  "one.js": "/******/ (() => { // webpackBootstrap
-
-/******/ })()
-;",
-  "two.js": "/******/ (() => { // webpackBootstrap
-
-/******/ })()
-;",
+  "one.js": "",
+  "two.js": "",
 }
 `;
 
@@ -3406,14 +3410,8 @@ exports[`TerserPlugin should write stdout and stderr of workers to stdout and st
 
 exports[`TerserPlugin should write stdout and stderr of workers to stdout and stderr of main process in parallel mode: assets 1`] = `
 Object {
-  "one.js": "/******/ (() => { // webpackBootstrap
-
-/******/ })()
-;",
-  "two.js": "/******/ (() => { // webpackBootstrap
-
-/******/ })()
-;",
+  "one.js": "",
+  "two.js": "",
 }
 `;