Allow transformers to return an empty string

src/utils/transform.ts

@@ -76,21 +76,21 @@ export default function transform(
 			}
 		}
 
-		if (!result) return code;
-
 		if (typeof result === 'string') {
 			result = {
 				ast: undefined,
 				code: result,
 				map: undefined
 			};
-		} else {
+		} else if (result && typeof result === 'object') {
 			if (typeof result.map === 'string') {
 				result.map = JSON.parse(result.map);
 			}
 			if (typeof result.moduleSideEffects === 'boolean') {
 				moduleSideEffects = result.moduleSideEffects;
 			}
+		} else {
+			return code;
 		}
 
 		if (result.map && typeof (result.map as ExistingRawSourceMap).mappings === 'string') {

test/function/samples/transform-empty-string/_config.js

@@ -0,0 +1,21 @@
+const assert = require('assert');
+
+const sideEffects = [];
+
+module.exports = {
+	description: 'allows transformers to transform code to an empty string',
+	context: { sideEffects },
+	exports() {
+		assert.deepStrictEqual(sideEffects, ['this happens']);
+	},
+	options: {
+		plugins: {
+			name: 'test-plugin',
+			transform(code, id) {
+				if (id.endsWith('transformed.js')) {
+					return '';
+				}
+			}
+		}
+	}
+};

test/function/samples/transform-empty-string/main.js

@@ -0,0 +1,3 @@
+import './transformed.js';
+
+sideEffects.push('this happens');

test/function/samples/transform-empty-string/transformed.js

@@ -0,0 +1 @@
+sideEffects.push('should not happen');