diff --git a/.prettierrc b/.prettierrc
new file mode 100644
index 0000000..5e13045
--- /dev/null
+++ b/.prettierrc
@@ -0,0 +1,9 @@
+{
+  "printWidth": 100,
+  "tabWidth": 2,
+  "singleQuote": true,
+  "trailingComma": "es5",
+  "semi": false,
+  "bracketSpacing": true,
+  "quoteProps": "consistent"
+}
diff --git a/dist/index.cjs.js b/dist/index.cjs.js
index 07c60a4..16b3b43 100644
--- a/dist/index.cjs.js
+++ b/dist/index.cjs.js
@@ -38,7 +38,7 @@ function isNull(payload) {
 function isPlainObject(payload) {
     if (getType(payload) !== 'Object')
         return false;
-    return (payload.constructor === Object && Object.getPrototypeOf(payload) === Object.prototype);
+    return payload.constructor === Object && Object.getPrototypeOf(payload) === Object.prototype;
 }
 /**
  * Returns whether the payload is a plain JavaScript object (excluding special classes or objects with other prototypes)
@@ -124,7 +124,7 @@ function isEmptyString(payload) {
  * @returns {payload is number}
  */
 function isNumber(payload) {
-    return (getType(payload) === 'Number' && !isNaN(payload));
+    return getType(payload) === 'Number' && !isNaN(payload);
 }
 /**
  * Returns whether the payload is a boolean
@@ -151,7 +151,7 @@ function isRegExp(payload) {
  * @returns {payload is symbol}
  */
 function isSymbol(payload) {
-    return (getType(payload) === 'Symbol');
+    return getType(payload) === 'Symbol';
 }
 /**
  * Returns whether the payload is a date, and that the date is Valid
@@ -160,7 +160,7 @@ function isSymbol(payload) {
  * @returns {payload is Date}
  */
 function isDate(payload) {
-    return (getType(payload) === 'Date' && !isNaN(payload));
+    return getType(payload) === 'Date' && !isNaN(payload);
 }
 /**
  * Returns whether the payload is a blob
@@ -194,6 +194,15 @@ function isPrimitive(payload) {
         isString(payload) ||
         isSymbol(payload));
 }
+/**
+ * Returns true whether the payload is null or undefined
+ *
+ * @param {*} payload
+ * @returns {(payload is null | undefined)}
+ */
+function isNullOrUndefined(payload) {
+    return isNull(payload) || isUndefined(payload);
+}
 /**
  * Does a generic check to check that the given payload is of a given type.
  * In cases like Number, it will return true for NaN as NaN is a Number (thanks javascript!);
@@ -214,7 +223,7 @@ function isType(payload, type) {
     }
     // Classes usually have names (as functions usually have names)
     var name = type.name;
-    return (getType(payload) === name) || Boolean(payload && (payload.constructor === type));
+    return getType(payload) === name || Boolean(payload && payload.constructor === type);
 }
 
 exports.getType = getType;
@@ -228,6 +237,7 @@ exports.isFile = isFile;
 exports.isFullString = isFullString;
 exports.isFunction = isFunction;
 exports.isNull = isNull;
+exports.isNullOrUndefined = isNullOrUndefined;
 exports.isNumber = isNumber;
 exports.isObject = isObject;
 exports.isObjectLike = isObjectLike;
diff --git a/dist/index.esm.js b/dist/index.esm.js
index 55bd53f..a9decb2 100644
--- a/dist/index.esm.js
+++ b/dist/index.esm.js
@@ -34,7 +34,7 @@ function isNull(payload) {
 function isPlainObject(payload) {
     if (getType(payload) !== 'Object')
         return false;
-    return (payload.constructor === Object && Object.getPrototypeOf(payload) === Object.prototype);
+    return payload.constructor === Object && Object.getPrototypeOf(payload) === Object.prototype;
 }
 /**
  * Returns whether the payload is a plain JavaScript object (excluding special classes or objects with other prototypes)
@@ -120,7 +120,7 @@ function isEmptyString(payload) {
  * @returns {payload is number}
  */
 function isNumber(payload) {
-    return (getType(payload) === 'Number' && !isNaN(payload));
+    return getType(payload) === 'Number' && !isNaN(payload);
 }
 /**
  * Returns whether the payload is a boolean
@@ -147,7 +147,7 @@ function isRegExp(payload) {
  * @returns {payload is symbol}
  */
 function isSymbol(payload) {
-    return (getType(payload) === 'Symbol');
+    return getType(payload) === 'Symbol';
 }
 /**
  * Returns whether the payload is a date, and that the date is Valid
@@ -156,7 +156,7 @@ function isSymbol(payload) {
  * @returns {payload is Date}
  */
 function isDate(payload) {
-    return (getType(payload) === 'Date' && !isNaN(payload));
+    return getType(payload) === 'Date' && !isNaN(payload);
 }
 /**
  * Returns whether the payload is a blob
@@ -190,6 +190,15 @@ function isPrimitive(payload) {
         isString(payload) ||
         isSymbol(payload));
 }
+/**
+ * Returns true whether the payload is null or undefined
+ *
+ * @param {*} payload
+ * @returns {(payload is null | undefined)}
+ */
+function isNullOrUndefined(payload) {
+    return isNull(payload) || isUndefined(payload);
+}
 /**
  * Does a generic check to check that the given payload is of a given type.
  * In cases like Number, it will return true for NaN as NaN is a Number (thanks javascript!);
@@ -210,7 +219,7 @@ function isType(payload, type) {
     }
     // Classes usually have names (as functions usually have names)
     var name = type.name;
-    return (getType(payload) === name) || Boolean(payload && (payload.constructor === type));
+    return getType(payload) === name || Boolean(payload && payload.constructor === type);
 }
 
-export { getType, isAnyObject, isArray, isBlob, isBoolean, isDate, isEmptyString, isFile, isFullString, isFunction, isNull, isNumber, isObject, isObjectLike, isPlainObject, isPrimitive, isRegExp, isString, isSymbol, isType, isUndefined };
+export { getType, isAnyObject, isArray, isBlob, isBoolean, isDate, isEmptyString, isFile, isFullString, isFunction, isNull, isNullOrUndefined, isNumber, isObject, isObjectLike, isPlainObject, isPrimitive, isRegExp, isString, isSymbol, isType, isUndefined };
diff --git a/package.json b/package.json
index ed266ab..237fce5 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "is-what",
-  "version": "3.4.0",
+  "version": "3.5.0",
   "description": "JS type check (TypeScript supported) functions like `isPlainObject() isArray()` etc. A simple & small integration.",
   "main": "dist/index.cjs.js",
   "module": "dist/index.esm.js",
diff --git a/src/index.ts b/src/index.ts
index f20a8bc..c8c5925 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -34,9 +34,9 @@ export function isNull (payload: any): payload is null {
  * @param {*} payload
  * @returns {payload is {[key: string]: any}}
  */
-export function isPlainObject (payload: any): payload is {[key: string]: any} {
+export function isPlainObject (payload: any): payload is { [key: string]: any } {
   if (getType(payload) !== 'Object') return false
-  return (payload.constructor === Object && Object.getPrototypeOf(payload) === Object.prototype)
+  return payload.constructor === Object && Object.getPrototypeOf(payload) === Object.prototype
 }
 
 /**
@@ -45,7 +45,7 @@ export function isPlainObject (payload: any): payload is {[key: string]: any} {
  * @param {*} payload
  * @returns {payload is {[key: string]: any}}
  */
-export function isObject (payload: any): payload is {[key: string]: any} {
+export function isObject (payload: any): payload is { [key: string]: any } {
   return isPlainObject(payload)
 }
 
@@ -55,7 +55,7 @@ export function isObject (payload: any): payload is {[key: string]: any} {
  * @param {*} payload
  * @returns {payload is {[key: string]: any}}
  */
-export function isAnyObject (payload: any): payload is {[key: string]: any} {
+export function isAnyObject (payload: any): payload is { [key: string]: any } {
   return getType(payload) === 'Object'
 }
 
@@ -131,7 +131,7 @@ export function isEmptyString (payload: any): payload is string {
  * @returns {payload is number}
  */
 export function isNumber (payload: any): payload is number {
-  return (getType(payload) === 'Number' && !isNaN(payload))
+  return getType(payload) === 'Number' && !isNaN(payload)
 }
 
 /**
@@ -161,7 +161,7 @@ export function isRegExp (payload: any): payload is RegExp {
  * @returns {payload is symbol}
  */
 export function isSymbol (payload: any): payload is symbol {
-  return (getType(payload) === 'Symbol')
+  return getType(payload) === 'Symbol'
 }
 
 /**
@@ -171,7 +171,7 @@ export function isSymbol (payload: any): payload is symbol {
  * @returns {payload is Date}
  */
 export function isDate (payload: any): payload is Date {
-  return (getType(payload) === 'Date' && !isNaN(payload))
+  return getType(payload) === 'Date' && !isNaN(payload)
 }
 
 /**
@@ -200,7 +200,9 @@ export function isFile (payload: any): payload is File {
  * @param {*} payload
  * @returns {(payload is boolean | null | undefined | number | string | symbol)}
  */
-export function isPrimitive (payload: any): payload is boolean | null | undefined | number | string | symbol {
+export function isPrimitive (
+  payload: any
+): payload is boolean | null | undefined | number | string | symbol {
   return (
     isBoolean(payload) ||
     isNull(payload) ||
@@ -211,6 +213,16 @@ export function isPrimitive (payload: any): payload is boolean | null | undefine
   )
 }
 
+/**
+ * Returns true whether the payload is null or undefined
+ *
+ * @param {*} payload
+ * @returns {(payload is null | undefined)}
+ */
+export function isNullOrUndefined (payload: any): payload is null | undefined {
+  return isNull(payload) || isUndefined(payload)
+}
+
 /**
  * Does a generic check to check that the given payload is of a given type.
  * In cases like Number, it will return true for NaN as NaN is a Number (thanks javascript!);
@@ -231,5 +243,5 @@ export function isType<T extends Function> (payload: any, type: T): payload is T
   }
   // Classes usually have names (as functions usually have names)
   const name: string | undefined | null = (<any>type).name
-  return (getType(payload) === name) || Boolean(payload && (payload.constructor === type))
+  return getType(payload) === name || Boolean(payload && payload.constructor === type)
 }
diff --git a/test/index.test.js b/test/index.test.js
index 0da602d..848cd9e 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -4,6 +4,7 @@ import {
   isAnyObject,
   isUndefined,
   isNull,
+  isNullOrUndefined,
   isFunction,
   isArray,
   isString,
@@ -23,6 +24,8 @@ import {
 test('Basic true tests', () => {
   expect(isUndefined(undefined)).toBe(true)
   expect(isNull(null)).toBe(true)
+  expect(isNullOrUndefined(null)).toBe(true)
+  expect(isNullOrUndefined(undefined)).toBe(true)
   expect(isObject({})).toBe(true)
   expect(isObject(new Object())).toBe(true)
   expect(isFunction(_ => {})).toBe(true)
@@ -59,6 +62,7 @@ test('Basic false tests', () => {
   expect(isBoolean(NaN)).toBe(false)
   expect(isRegExp(NaN)).toBe(false)
   expect(isSymbol(NaN)).toBe(false)
+  expect(isNullOrUndefined(NaN)).toBe(false)
 })
 
 test('Primitive tests', () => {
@@ -131,7 +135,11 @@ test('isObject vs isAnyObject', () => {
   class MyClass2 {}
   const myClass2 = new MyClass()
   const mySpecialObject = {}
-  Object.setPrototypeOf(mySpecialObject, {toDate: function () { return new Date() }})
+  Object.setPrototypeOf(mySpecialObject, {
+    toDate: function () {
+      return new Date()
+    },
+  })
   // IS OBJECT
   // plain object
   expect(isObject({})).toBe(true)
diff --git a/types/index.d.ts b/types/index.d.ts
index 39822ce..82a9770 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -149,6 +149,13 @@ export declare function isFile(payload: any): payload is File;
  * @returns {(payload is boolean | null | undefined | number | string | symbol)}
  */
 export declare function isPrimitive(payload: any): payload is boolean | null | undefined | number | string | symbol;
+/**
+ * Returns true whether the payload is null or undefined
+ *
+ * @param {*} payload
+ * @returns {(payload is null | undefined)}
+ */
+export declare function isNullOrUndefined(payload: any): payload is null | undefined;
 /**
  * Does a generic check to check that the given payload is of a given type.
  * In cases like Number, it will return true for NaN as NaN is a Number (thanks javascript!);