Major refactoring

readme.md

@@ -154,7 +154,7 @@ Default: `{}`
 
 Request headers.
 
-Existing headers will be overwritten. Headers set to `null` will be omitted.
+Existing headers will be overwritten. Headers set to `undefined` will be omitted.
 
 ###### isStream
 
@@ -1311,7 +1311,7 @@ const got = require('got');
 
 ### User Agent
 
-It's a good idea to set the `'user-agent'` header so the provider can more easily see how their resource is used. By default, it's the URL to this repo. You can omit this header by setting it to `undefined` (or `null`).
+It's a good idea to set the `'user-agent'` header so the provider can more easily see how their resource is used. By default, it's the URL to this repo. You can omit this header by setting it to `undefined`.
 
 ```js
 const got = require('got');

source/normalize-arguments.ts

@@ -253,8 +253,10 @@ export const normalizeArguments = (url: URLOrOptions, options?: Options, default
 
 	// Make it possible to remove default headers
 	for (const [key, value] of Object.entries(options.headers)) {
-		if (is.nullOrUndefined(value)) {
+		if (is.undefined(value)) {
 			delete options.headers[key];
+		} else if (is.null_(value)) {
+			throw new TypeError('Use `undefined` instead of `null` to delete HTTP headers');
 		}
 	}
 
@@ -405,5 +407,8 @@ export const normalizeRequestArguments = async (options: NormalizedOptions): Pro
 
 	delete options.timeout;
 
+	// `http-cache-semantics` check this
+	delete options.url;
+
 	return options as unknown as NormalizedRequestArguments;
 };

source/request-as-event-emitter.ts

@@ -230,8 +230,7 @@ export default (options: NormalizedOptions) => {
 			// `cacheable-request` doesn't support Node 10 API, fallback.
 			httpOptions = {
 				...httpOptions,
-				...urlToOptions(options.url),
-				url: undefined // `http-cache-semantics` check this
+				...urlToOptions(options.url)
 			};
 
 			const cacheRequest = options.cacheableRequest(httpOptions, handleResponse);

test/headers.ts

@@ -183,16 +183,12 @@ test('buffer as `options.body` sets `content-length` header', withServer, async
 	t.is(Number(headers['content-length']), buffer.length);
 });
 
-test('removes null value headers', withServer, async (t, server, got) => {
-	server.get('/', echoHeaders);
-
-	const {body} = await got({
+test('throws on null value headers', async t => {
+	await t.throwsAsync(got({
 		headers: {
 			'user-agent': null
 		}
-	});
-	const headers = JSON.parse(body);
-	t.false(Reflect.has(headers, 'user-agent'));
+	}), TypeError, 'Use `undefined` instead of `null` to delete HTTP headers');
 });
 
 test('removes undefined value headers', withServer, async (t, server, got) => {