@@ -0,0 +1,5 @@
+---
+"webpack": patch
+---
+
+Preserve empty process environment variables in `DotenvPlugin`.
@@ -509,7 +509,7 @@ class DotenvPlugin {
 			if (prefixes.some((prefix) => key.startsWith(prefix))) {
 				env[key] =
 					Object.prototype.hasOwnProperty.call(process.env, key) &&
-					process.env[key]
+					process.env[key] !== undefined
 						? process.env[key]
 						: parsed[key];
 			}
 
@@ -0,0 +1,2 @@
+WEBPACK_DOTENV_EMPTY_OVERRIDE=from-file
+WEBPACK_DOTENV_NONEMPTY=from-file
@@ -0,0 +1,22 @@
+"use strict";
+
+it("should preserve empty process variables without a file default", () => {
+	expect(process.env.WEBPACK_DOTENV_EMPTY_PROCESS_ONLY).toBe("");
+	expect(import.meta.env.WEBPACK_DOTENV_EMPTY_PROCESS_ONLY).toBe("");
+	expect(
+		Object.prototype.hasOwnProperty.call(
+			import.meta.env,
+			"WEBPACK_DOTENV_EMPTY_PROCESS_ONLY"
+		)
+	).toBe(true);
+});
+
+it("should let empty process variables override file values", () => {
+	expect(process.env.WEBPACK_DOTENV_EMPTY_OVERRIDE).toBe("");
+	expect(import.meta.env.WEBPACK_DOTENV_EMPTY_OVERRIDE).toBe("");
+});
+
+it("should preserve nonempty process variables", () => {
+	expect(process.env.WEBPACK_DOTENV_NONEMPTY).toBe("from-process");
+	expect(import.meta.env.WEBPACK_DOTENV_NONEMPTY).toBe("from-process");
+});
@@ -0,0 +1,43 @@
+"use strict";
+
+/**
+ * @param {import("../../../../").Compiler} compiler compiler
+ * @returns {void}
+ */
+const setProcessEnv = (compiler) => {
+	const values = {
+		WEBPACK_DOTENV_EMPTY_PROCESS_ONLY: "",
+		WEBPACK_DOTENV_EMPTY_OVERRIDE: "",
+		WEBPACK_DOTENV_NONEMPTY: "from-process"
+	};
+	/** @type {Map<string, string | undefined>} */
+	const previousValues = new Map();
+
+	compiler.hooks.beforeCompile.tap("TestEmptyProcessEnv", () => {
+		for (const [key, value] of Object.entries(values)) {
+			previousValues.set(key, process.env[key]);
+			process.env[key] = value;
+		}
+	});
+	compiler.hooks.afterCompile.tap("TestEmptyProcessEnv", () => {
+		for (const [key, value] of previousValues) {
+			if (value === undefined) {
+				delete process.env[key];
+			} else {
+				process.env[key] = value;
+			}
+		}
+	});
+};
+
+/** @type {import("../../../../").Configuration[]} */
+module.exports = [
+	{
+		dotenv: true,
+		plugins: [setProcessEnv]
+	},
+	{
+		dotenv: { dir: false },
+		plugins: [setProcessEnv]
+	}
+];
-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +---
 +"webpack": patch
 +---
++
 +Preserve empty process environment variables in `DotenvPlugin`.
Original file line number	Diff line number	Diff line change
`@@ -509,7 +509,7 @@ class DotenvPlugin {`
`509`	`509`	`if (prefixes.some((prefix) => key.startsWith(prefix))) {`
`510`	`510`	`env[key] =`
`511`	`511`	`Object.prototype.hasOwnProperty.call(process.env, key) &&`
`512`		`- process.env[key]`
	`512`	`+ process.env[key] !== undefined`
`513`	`513`	`? process.env[key]`
`514`	`514`	`: parsed[key];`
`515`	`515`	`}`
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	`+WEBPACK_DOTENV_EMPTY_OVERRIDE=from-file`
	`2`	`+WEBPACK_DOTENV_NONEMPTY=from-file`