Description:
------------
When using Reflections and accessing the method return type or parameter type, php crashes might crash if the parameter is nullable.
The first checked class works flawless, the second class produces the crash.

Test script:
---------------
<?php

function randomName(int $length) : string
{
    return implode('', array_map(function () : string {
        return chr(65 + rand(0, 25) + (rand(0, 1) === 0 ? 0 : 32));
    }, array_fill(0, $length, '')));
}

function createTestClass(int $classNameLength, int $numMethods, int $methodNameLength) : string
{
    do {
        $className = randomName($classNameLength);
    } while (class_exists($className));

    $methods = [];

    for ($m = 0; $m < $numMethods; $m++) {
        do {
            $methodName = randomName($methodNameLength);
        } while (array_key_exists($methodName, $methods));

        $methods[$methodName] = 'public function ' . $methodName . '(?string $param) : ?string { return $param; }';
    }

    eval(implode(PHP_EOL, ['class ' . $className . '{', implode(PHP_EOL, $methods), '}']));

    return $className;
}

function testClassReflections(string $className) : void
{
    $class = new ReflectionClass($className);
    $methods = [];

    foreach ($class->getMethods() as $method) {
        $parameters = [];

        foreach ($method->getParameters() as $parameter) {
            $parameters[] = $parameter->getType() . ' ' . $parameter->getName();
        }

        $methods[] = $method->getReturnType() . ' ' . $method->getName() . '(' . implode(', ', $parameters) . ')';
    }

    printf('%s { %s }' . PHP_EOL, $class->getName(), implode(', ', $methods));
}

function test(int $numClasses, int $classNameLength, int $numMethods, int $methodNameLength) : void
{

    printf('{ classes: { num: %d, length: %d }, methods: { num: %d, length: %d } }' . PHP_EOL,
        $numClasses, $classNameLength, $numMethods, $methodNameLength
    );

    for ($c = 0; $c < $numClasses; $c++) {
        testClassReflections(createTestClass($classNameLength, $numMethods, $methodNameLength));
    }
}

// This does not crash when first parameter is 1.
test(2, 10, 5, 10);