Update isFunction.md

snippets/isFunction.md

@@ -5,10 +5,11 @@ Checks if the given argument is a function.
 Use `typeof` to check if a value is classified as a function primitive.
 
 ```js
-const isFunction = val => val && typeof val === 'function';
+const isFunction = val => typeof val === 'function';
 ```
 
 ```js
+isFunction(null); // false
 isFunction('x'); // false
 isFunction(x => x); // true
 ```