Fix prefixUrl not working when the url argument is empty

Fixes #1322

source/core/index.ts

@@ -619,13 +619,13 @@ export default class Request extends Duplex implements RequestEvents<Request> {
 		if (is.object(url) && !is.urlInstance(url)) {
 			options = {...defaults, ...(url as Options), ...options};
 		} else {
-			if (url && options && options.url) {
+			if (url && options && options.url !== undefined) {
 				throw new TypeError('The `url` option is mutually exclusive with the `input` argument');
 			}
 
 			options = {...defaults, ...options};
 
-			if (url) {
+			if (url !== undefined) {
 				options.url = url;
 			}
 

test/arguments.ts

@@ -12,12 +12,20 @@ const echoUrl: Handler = (request, response) => {
 
 test('`url` is required', async t => {
 	await t.throwsAsync(
-		got(''),
+		// @ts-ignore No argument on purpose.
+		got(),
 		{
 			message: 'Missing `url` property'
 		}
 	);
 
+	await t.throwsAsync(
+		got(''),
+		{
+			message: 'No URL protocol specified'
+		}
+	);
+
 	await t.throwsAsync(
 		got({
 			url: ''
@@ -541,3 +549,18 @@ test('no URL pollution', withServer, async (t, server) => {
 	t.is(url.pathname, '/');
 	t.is(body, '/ok');
 });
+
+test('prefixUrl is properly replaced when extending', withServer, async (t, server) => {
+	server.get('/', (request, response) => {
+		response.end(request.url);
+	});
+
+	server.get('/other/path/', (request, response) => {
+		response.end(request.url);
+	});
+
+	const parent = got.extend({ prefixUrl: server.url });
+	const child = parent.extend({ prefixUrl: `${server.url}/other/path/` });
+
+	t.is(await child.get('').text(), '/other/path/');
+});