Add null coalescing section

README.md

@@ -16,6 +16,7 @@
      * [Use default arguments instead of short circuiting or conditionals](#use-default-arguments-instead-of-short-circuiting-or-conditionals)
   3. [Comparison](#comparison)
      * [Use identical comparison](#use-identical-comparison)
+     * [Null coalescing operator](#null-coalescing-operator)
   4. [Functions](#functions)
      * [Function arguments (2 or fewer ideally)](#function-arguments-2-or-fewer-ideally)
      * [Function names should say what they do](#function-names-should-say-what-they-do)
@@ -440,6 +441,28 @@ The comparison `$a !== $b` returns `TRUE`.
 
 **[⬆ back to top](#table-of-contents)**
 
+### Null coalescing operator
+
+Null coalescing is a new operator [introduced in PHP 7](https://www.php.net/manual/en/migration70.new-features.php). The null coalescing operator `??` has been added as syntactic sugar for the common case of needing to use a ternary in conjunction with `isset()`. It returns its first operand if it exists and is not `null`; otherwise it returns its second operand.
+
+**Bad:**
+
+```php
+if (isset($_GET['name'])) {
+    $name = $_GET['name'];
+} elseif (isset($_POST['name'])) {
+    $name = $_POST['name'];
+} else {
+    $name = 'nobody';
+}
+```
+
+**Good:**
+```php
+$name = $_GET['name'] ?? $_POST['name'] ?? 'nobody';
+```
+
+**[⬆ back to top](#table-of-contents)**
 
 ## Functions