diff --git a/src/Config/SDK/Configuration/Loader/YamlExtensionFileLoader.php b/src/Config/SDK/Configuration/Loader/YamlExtensionFileLoader.php
index 8a97c8f17..9356dcb4d 100644
--- a/src/Config/SDK/Configuration/Loader/YamlExtensionFileLoader.php
+++ b/src/Config/SDK/Configuration/Loader/YamlExtensionFileLoader.php
@@ -18,12 +18,12 @@
 final class YamlExtensionFileLoader extends FileLoader
 {
 
-    public function __construct(private readonly ConfigurationLoader $configuration, FileLocatorInterface $locator, string $env = null)
+    public function __construct(private readonly ConfigurationLoader $configuration, FileLocatorInterface $locator, ?string $env = null)
     {
         parent::__construct($locator, $env);
     }
 
-    public function load(mixed $resource, string $type = null): mixed
+    public function load(mixed $resource, ?string $type = null): mixed
     {
         assert(extension_loaded('yaml'));
 
@@ -39,7 +39,7 @@ public function load(mixed $resource, string $type = null): mixed
         return null;
     }
 
-    public function supports(mixed $resource, string $type = null): bool
+    public function supports(mixed $resource, ?string $type = null): bool
     {
         return extension_loaded('yaml')
             && is_string($resource)
diff --git a/src/Config/SDK/Configuration/Loader/YamlSymfonyFileLoader.php b/src/Config/SDK/Configuration/Loader/YamlSymfonyFileLoader.php
index 25d1b02d3..222839144 100644
--- a/src/Config/SDK/Configuration/Loader/YamlSymfonyFileLoader.php
+++ b/src/Config/SDK/Configuration/Loader/YamlSymfonyFileLoader.php
@@ -20,12 +20,12 @@
 final class YamlSymfonyFileLoader extends FileLoader
 {
 
-    public function __construct(private readonly ConfigurationLoader $configuration, FileLocatorInterface $locator, string $env = null)
+    public function __construct(private readonly ConfigurationLoader $configuration, FileLocatorInterface $locator, ?string $env = null)
     {
         parent::__construct($locator, $env);
     }
 
-    public function load(mixed $resource, string $type = null): mixed
+    public function load(mixed $resource, ?string $type = null): mixed
     {
         assert(class_exists(Yaml::class));
 
@@ -43,7 +43,7 @@ public function load(mixed $resource, string $type = null): mixed
         return null;
     }
 
-    public function supports(mixed $resource, string $type = null): bool
+    public function supports(mixed $resource, ?string $type = null): bool
     {
         return class_exists(Yaml::class)
             && is_string($resource)
diff --git a/tests/Unit/SDK/Metrics/MeterTest.php b/tests/Unit/SDK/Metrics/MeterTest.php
index fa6fd83a7..02af7e0ef 100644
--- a/tests/Unit/SDK/Metrics/MeterTest.php
+++ b/tests/Unit/SDK/Metrics/MeterTest.php
@@ -376,7 +376,7 @@ public function test_uses_default_view_if_null_views_returned(): void
     /**
      * @param iterable<MetricReaderInterface&MetricSourceRegistryInterface&DefaultAggregationProviderInterface> $metricReaders
      */
-    private function createMeterProviderForMetricFactory(MetricFactoryInterface $metricFactory, ViewRegistryInterface $viewRegistry = null, iterable $metricReaders = []): MeterProvider
+    private function createMeterProviderForMetricFactory(MetricFactoryInterface $metricFactory, ?ViewRegistryInterface $viewRegistry = null, iterable $metricReaders = []): MeterProvider
     {
         return new MeterProvider(
             null,
diff --git a/tests/Unit/SDK/Trace/SamplerFactoryTest.php b/tests/Unit/SDK/Trace/SamplerFactoryTest.php
index 6e73906a1..52534046a 100644
--- a/tests/Unit/SDK/Trace/SamplerFactoryTest.php
+++ b/tests/Unit/SDK/Trace/SamplerFactoryTest.php
@@ -17,7 +17,7 @@ class SamplerFactoryTest extends TestCase
     use TestState;
 
     #[DataProvider('samplerProvider')]
-    public function test_create_sampler_from_environment(string $samplerName, string $expected, string $arg = null): void
+    public function test_create_sampler_from_environment(string $samplerName, string $expected, ?string $arg = null): void
     {
         $this->setEnvironmentVariable('OTEL_TRACES_SAMPLER', $samplerName);
         $this->setEnvironmentVariable('OTEL_TRACES_SAMPLER_ARG', $arg);
@@ -39,7 +39,7 @@ public static function samplerProvider(): array
         ];
     }
     #[DataProvider('invalidSamplerProvider')]
-    public function test_throws_exception_for_invalid_or_unsupported(?string $sampler, string $arg = null): void
+    public function test_throws_exception_for_invalid_or_unsupported(?string $sampler, ?string $arg = null): void
     {
         $this->setEnvironmentVariable('OTEL_TRACES_SAMPLER', $sampler);
         $this->setEnvironmentVariable('OTEL_TRACES_SAMPLER_ARG', $arg);
diff --git a/tests/Unit/SDK/Trace/SpanExporter/FriendlySpanConverterTest.php b/tests/Unit/SDK/Trace/SpanExporter/FriendlySpanConverterTest.php
index 118ae66db..95285378c 100644
--- a/tests/Unit/SDK/Trace/SpanExporter/FriendlySpanConverterTest.php
+++ b/tests/Unit/SDK/Trace/SpanExporter/FriendlySpanConverterTest.php
@@ -178,7 +178,7 @@ private function createInstrumentationScopeMock(): InstrumentationScopeInterface
 
         return $mock;
     }
-    private function createSpanContextMock(string $spanId, string $traceId = '0', string $traceState = null): SpanContextInterface
+    private function createSpanContextMock(string $spanId, string $traceId = '0', ?string $traceState = null): SpanContextInterface
     {
         $mock = $this->createMock(SpanContextInterface::class);
 
diff --git a/tests/Unit/SDK/Trace/SpanTest.php b/tests/Unit/SDK/Trace/SpanTest.php
index a17dd1554..647558a5d 100644
--- a/tests/Unit/SDK/Trace/SpanTest.php
+++ b/tests/Unit/SDK/Trace/SpanTest.php
@@ -835,8 +835,8 @@ private function createTestRootSpan(): Span
      */
     private function createTestSpan(
         int $kind = API\SpanKind::KIND_INTERNAL,
-        SpanLimits $spanLimits = null,
-        string $parentSpanId = null,
+        ?SpanLimits $spanLimits = null,
+        ?string $parentSpanId = null,
         iterable $attributes = [],
         array $links = [],
     ): Span {
diff --git a/tests/Unit/SDK/Util/SpanData.php b/tests/Unit/SDK/Util/SpanData.php
index 1c77f5531..dc814f645 100644
--- a/tests/Unit/SDK/Util/SpanData.php
+++ b/tests/Unit/SDK/Util/SpanData.php
@@ -102,7 +102,7 @@ public function setEvents(array $events): self
         return $this;
     }
 
-    public function addEvent(string $name, AttributesInterface $attributes, int $timestamp = null): self
+    public function addEvent(string $name, AttributesInterface $attributes, ?int $timestamp = null): self
     {
         $this->events[] = new SDK\Event($name, $timestamp ?? Clock::getDefault()->now(), $attributes);