What are best practices for initializing variables in PHP to ensure code cleanliness and avoid errors?

When initializing variables in PHP, it is best practice to assign default values to avoid errors and ensure code cleanliness. This can be achieved by using the null coalescing operator (??) to set a default value if the variable is not already set. By doing this, you can prevent undefined variable errors and make your code more robust.

// Initializing a variable with a default value using the null coalescing operator
$variable = $_POST['value'] ?? 'default_value';