Make body default to null in Request

Fixes #208.

src/index.js

@@ -184,7 +184,7 @@ function fetch(url, opts) {
 			return;
 		});
 
-		// accept string, buffer or readable stream as body
+		// accept string, buffer, readable stream or null as body
 		// per spec we will call tostring on non-stream objects
 		if (typeof request.body === 'string') {
 			req.write(request.body);
@@ -192,9 +192,9 @@ function fetch(url, opts) {
 		} else if (request.body instanceof Buffer) {
 			req.write(request.body);
 			req.end()
-		} else if (typeof request.body === 'object' && request.body.pipe) {
+		} else if (request.body && typeof request.body === 'object' && request.body.pipe) {
 			request.body.pipe(req);
-		} else if (typeof request.body === 'object') {
+		} else if (request.body && typeof request.body === 'object') {
 			req.write(request.body.toString());
 			req.end();
 		} else {

src/request.js

@@ -40,12 +40,18 @@ export default class Request extends Body {
 
 		let method = init.method || input.method || 'GET';
 
-		if ((init.body != null || input instanceof Request && input.body != null) &&
+		if ((init.body != null || input instanceof Request && input.body !== null) &&
 			(method === 'GET' || method === 'HEAD')) {
 			throw new TypeError('Request with GET/HEAD method cannot have body');
 		}
 
-		super(init.body || clone(input), {
+		let inputBody = init.body != null ?
+			init.body :
+			input instanceof Request && input.body !== null ?
+				clone(input) :
+				null;
+
+		super(inputBody, {
 			timeout: init.timeout || input.timeout || 0,
 			size: init.size || input.size || 0
 		});

test/test.js

@@ -1544,9 +1544,14 @@ describe(`node-fetch with FOLLOW_SPEC = ${defaultFollowSpec}`, () => {
 	it('should default to null as body', function() {
 		const res = new Response();
 		expect(res.body).to.equal(null);
-		return res.text().then(result => {
-			expect(result).to.equal('');
-		});
+		const req = new Request('.');
+		expect(req.body).to.equal(null);
+
+		const cb = result => expect(result).to.equal('');
+		return Promise.all([
+			res.text().then(cb),
+			req.text().then(cb)
+		]);
 	});
 
 	it('should default to 200 as status code', function() {