Bad null guards can cause null pointer dereferences

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Metadata

ID: php-code-style/bad-null-guard

Language: PHP

Severity: Error

Category: Error Prone

Description

This rule checks for improper null guard conditions in PHP code. A null guard is a conditional statement that checks if a variable is null before proceeding with an operation. This is important to prevent null pointer dereferences, which occur when the program tries to access a memory location through a null pointer. Null pointer dereferences can lead to unexpected behaviors and crashes in your application.

In non-compliant code, the logical AND (&&) and OR (||) operators are used incorrectly in null guard conditions. This can lead to situations where a method is called on a null object, causing a null pointer dereference.

To avoid violating this rule, always use the correct logical operator in your null guard conditions. If you want to ensure that a method is only called when a variable is not null, use the AND operator (&&). If you want to ensure that a method is called when a variable is null or the method returns true, use the OR operator (||). This way, you can prevent null pointer dereferences and improve the robustness of your code.

Non-Compliant Code Examples

<?php
if ($var == null && $var->method()) {
  echo "method is true";
}

if ($var != null || $var->method()) {
  echo "method is true";
}

Compliant Code Examples

<?php
if ($var == null || $var->method()) {
  echo "method is true";
}

if ($var != null && $var->method()) {
  echo "method is true";
}