feat(isNil): Add module isNil

Checks if a value is null or undefined

src/__tests__/isNil.js

@@ -0,0 +1,12 @@
+import isNil from '../isNil';
+
+test('Core.isNil', () => {
+  expect(isNil(null)).toBeTruthy();
+  expect(isNil(undefined)).toBeTruthy();
+  expect(isNil(() => null)).toBeFalsy();
+  expect(isNil({})).toBeFalsy();
+  expect(isNil({ foo: 'bar' })).toBeFalsy();
+  expect(isNil([])).toBeFalsy();
+  expect(isNil('a')).toBeFalsy();
+  expect(isNil(1)).toBeFalsy();
+});

src/index.js

@@ -11,6 +11,7 @@ import head from './head';
 import is from './is';
 import isArray from './isArray';
 import isFunction from './isFunction';
+import isNil from './isNil';
 import isObject from './isObject';
 import last from './last';
 import map from './map';
@@ -36,6 +37,7 @@ export {
   is,
   isArray,
   isFunction,
+  isNil,
   isObject,
   last,
   map,

src/isNil.js

@@ -0,0 +1 @@
+export default x => x == null;