TypeError: Wrong Argument Type

Why This Happens

PHP 7+ enforces type declarations in function signatures when strict_types is enabled or for built-in type coercion failures. When you pass null to a string parameter or an array to an integer parameter, PHP throws a TypeError. This is especially common when database queries return null for missing fields.

The Problem

function createUser(string $name, string $email): void {
    // ...
}
$name = $_POST['name'] ?? null;
createUser($name, 'test@example.com');

The Fix

function createUser(string $name, string $email): void {
    // ...
}
$name = $_POST['name'] ?? '';
if ($name === '') {
    throw new InvalidArgumentException('Name is required');
}
createUser($name, 'test@example.com');

Step-by-Step Fix

1. 1

   Read the type mismatch

   The error message tells you which argument, what type was expected, and what type was actually given.

2. 2

   Trace the argument value

   Find where the variable gets its value and determine why it has the wrong type. Check for null returns, missing input, or incorrect casts.

3. 3

   Fix the type or the declaration

   Either validate and convert the value before passing it, or change the parameter to a nullable type (?string) if null is a valid input.