allow empty string as valid document content, fixes #6526

extensions/vscode-api-tests/src/workspace.test.ts

@@ -294,6 +294,23 @@ suite('workspace-namespace', () => {
 		});
 	});
 
+	test('registerTextDocumentContentProvider, empty doc', function () {
+
+		let registration = workspace.registerTextDocumentContentProvider('foo', {
+			provideTextDocumentContent(uri) {
+				return '';
+			}
+		});
+
+		const uri = Uri.parse('foo:doc/empty');
+
+		return workspace.openTextDocument(uri).then(doc => {
+			assert.equal(doc.getText(), '');
+			assert.equal(doc.uri.toString(), uri.toString());
+			registration.dispose();
+		});
+	});
+
 	test('registerTextDocumentContentProvider, change event', function () {
 
 		let callCount = 0;

src/vs/workbench/api/node/extHostDocuments.ts

@@ -631,7 +631,7 @@ export class MainThreadDocuments {
 		this._resourceContentProvider[handle] = ResourceEditorInput.registerResourceContentProvider(scheme, {
 			provideTextContent: (uri: URI): TPromise<EditorCommon.IModel> => {
 				return this._proxy.$provideTextDocumentContent(handle, uri).then(value => {
-					if (value) {
+					if (typeof value === 'string') {
 						this._virtualDocumentSet[uri.toString()] = true;
 						const firstLineText = value.substr(0, 1 + value.search(/\r?\n/));
 						const mode = this._modeService.getOrCreateModeByFilenameOrFirstLine(uri.fsPath, firstLineText);