Return undefined instead of null when gateway cannot be determined

index.d.ts

@@ -1,45 +1,57 @@
 interface v6 {
 	/**
-	 * @returns The IPv6 address of the internet-facing interface, as determined from the default gateway. When the address cannot be determined for any reason, `null` will be returned.
-	 *
-	 * @example
-	 *
-	 * console.log(await internalIp.v6());
-	 * //=> 'fe80::1'
-	 */
-	(): Promise<string>;
+	@returns The IPv6 address of the internet-facing interface, as determined from the default gateway. When the address cannot be determined for any reason, `undefined` will be returned.
+
+	@example
+	```
+	import internalIp = require('internal-ip');
+
+	console.log(await internalIp.v6());
+	//=> 'fe80::1'
+	```
+	*/
+	(): Promise<string | undefined>;
 
 	/**
-	 * @returns The IPv6 address of the internet-facing interface, as determined from the default gateway. When the address cannot be determined for any reason, `null` will be returned.
-	 *
-	 * @example
-	 *
-	 * console.log(internalIp.v6.sync());
-	 * //=> 'fe80::1'
-	 */
-	sync(): string;
+	@returns The IPv6 address of the internet-facing interface, as determined from the default gateway. When the address cannot be determined for any reason, `undefined` will be returned.
+
+	@example
+	```
+	import internalIp = require('internal-ip');
+
+	console.log(internalIp.v6.sync());
+	//=> 'fe80::1'
+	```
+	*/
+	sync(): string | undefined;
 }
 
 interface v4 {
 	/**
-	 * @returns The IPv4 address of the internet-facing interface, as determined from the default gateway. When the address cannot be determined for any reason, `null` will be returned.
-	 *
-	 * @example
-	 *
-	 * console.log(await internalIp.v4())
-	 * //=> '10.0.0.79'
-	 */
-	(): Promise<string>;
+	@returns The IPv4 address of the internet-facing interface, as determined from the default gateway. When the address cannot be determined for any reason, `undefined` will be returned.
+
+	@example
+	```
+	import internalIp = require('internal-ip');
+
+	console.log(await internalIp.v4())
+	//=> '10.0.0.79'
+	```
+	*/
+	(): Promise<string | undefined>;
 
 	/**
-	 * @returns The IPv4 address of the internet-facing interface, as determined from the default gateway. When the address cannot be determined for any reason, `null` will be returned.
-	 *
-	 * @example
-	 *
-	 * console.log(internalIp.v4.sync())
-	 * //=> '10.0.0.79'
-	 */
-	sync(): string;
+	@returns The IPv4 address of the internet-facing interface, as determined from the default gateway. When the address cannot be determined for any reason, `undefined` will be returned.
+
+	@example
+	```
+	import internalIp = require('internal-ip');
+
+	console.log(internalIp.v4.sync())
+	//=> '10.0.0.79'
+	```
+	*/
+	sync(): string | undefined;
 }
 
 declare const internalIp: {

index.js

@@ -28,19 +28,15 @@ function findIp(gateway) {
 async function promise(family) {
 	try {
 		const result = await defaultGateway[family]();
-		return findIp(result.gateway) || null;
-	} catch (_) {
-		return null;
-	}
+		return findIp(result.gateway);
+	} catch (_) {}
 }
 
 function sync(family) {
 	try {
 		const result = defaultGateway[family].sync();
-		return findIp(result.gateway) || null;
-	} catch (_) {
-		return null;
-	}
+		return findIp(result.gateway);
+	} catch (_) {}
 }
 
 const internalIp = {};

index.test-d.ts

@@ -1,8 +1,8 @@
 import {expectType} from 'tsd';
 import internalIp = require('.');
 
-expectType<string>(await internalIp.v4());
-expectType<string>(await internalIp.v6());
+expectType<string | undefined>(await internalIp.v4());
+expectType<string | undefined>(await internalIp.v6());
 
-expectType<string>(internalIp.v4.sync());
-expectType<string>(internalIp.v6.sync());
+expectType<string | undefined>(internalIp.v4.sync());
+expectType<string | undefined>(internalIp.v6.sync());

readme.md

@@ -30,7 +30,7 @@ console.log(internalIp.v4.sync())
 //=> '10.0.0.79'
 ```
 
-The module returns the address of the internet-facing interface, as determined from the default gateway. When the address cannot be determined for any reason, `null` will be returned.
+The module returns the address of the internet-facing interface, as determined from the default gateway. When the address cannot be determined for any reason, `undefined` will be returned.
 
 The module relies on operating systems tools. On Linux and Android, the `ip` command must be available, which depending on distribution might not be installed by default. It is usually provided by the `iproute2` package.
 

test.js

@@ -2,14 +2,14 @@ import {isIPv4, isIPv6} from 'net';
 import test from 'ava';
 import internalIp from '.';
 
-// Travis VMs don't have IPs on their interfaces
+// Travis VMs don't have IPs on their interfaces.
 // https://docs.travis-ci.com/user/ci-environment/#Networking
 const isCI = Boolean(process.env.CI);
 
 test('IPv6', async t => {
 	const ip = await internalIp.v6();
 	if (isCI) {
-		t.is(ip, null);
+		t.is(ip, undefined);
 	} else {
 		t.true(isIPv6(ip));
 	}
@@ -18,7 +18,7 @@ test('IPv6', async t => {
 test('IPv4', async t => {
 	const ip = await internalIp.v4();
 	if (isCI) {
-		t.is(ip, null);
+		t.is(ip, undefined);
 	} else {
 		t.true(isIPv4(ip));
 	}
@@ -27,7 +27,7 @@ test('IPv4', async t => {
 test('synchronous IPv6', t => {
 	const ip = internalIp.v6.sync();
 	if (isCI) {
-		t.is(ip, null);
+		t.is(ip, undefined);
 	} else {
 		t.true(isIPv6(ip));
 	}
@@ -36,7 +36,7 @@ test('synchronous IPv6', t => {
 test('synchronous IPv4', t => {
 	const ip = internalIp.v4.sync();
 	if (isCI) {
-		t.is(ip, null);
+		t.is(ip, undefined);
 	} else {
 		t.true(isIPv4(ip));
 	}