What are some common mistakes or pitfalls that beginners might encounter when working with PHP functions and return values?

Beginners might encounter issues with returning values from functions, such as not properly returning a value or returning the wrong data type. To solve this, always ensure that your function explicitly returns a value using the `return` keyword, and make sure the returned value matches the expected data type.

// Incorrect way of returning a value
function addNumbers($num1, $num2) {
    $sum = $num1 + $num2; // missing return statement
}

// Correct way of returning a value
function addNumbers($num1, $num2) {
    $sum = $num1 + $num2;
    return $sum;
}