diff --git a/src/API/Baggage/Propagation/BaggagePropagator.php b/src/API/Baggage/Propagation/BaggagePropagator.php
index 964868705..788db2ae1 100644
--- a/src/API/Baggage/Propagation/BaggagePropagator.php
+++ b/src/API/Baggage/Propagation/BaggagePropagator.php
@@ -39,7 +39,7 @@ public function fields(): array
         return [self::BAGGAGE];
     }
 
-    public function inject(&$carrier, PropagationSetterInterface $setter = null, ContextInterface $context = null): void
+    public function inject(&$carrier, ?PropagationSetterInterface $setter = null, ?ContextInterface $context = null): void
     {
         $setter ??= ArrayAccessGetterSetter::getInstance();
         $context ??= Context::getCurrent();
@@ -70,7 +70,7 @@ public function inject(&$carrier, PropagationSetterInterface $setter = null, Con
         }
     }
 
-    public function extract($carrier, PropagationGetterInterface $getter = null, ContextInterface $context = null): ContextInterface
+    public function extract($carrier, ?PropagationGetterInterface $getter = null, ?ContextInterface $context = null): ContextInterface
     {
         $getter ??= ArrayAccessGetterSetter::getInstance();
         $context ??= Context::getCurrent();
diff --git a/src/API/Trace/Propagation/TraceContextPropagator.php b/src/API/Trace/Propagation/TraceContextPropagator.php
index b70a15647..e1cc7e3dc 100644
--- a/src/API/Trace/Propagation/TraceContextPropagator.php
+++ b/src/API/Trace/Propagation/TraceContextPropagator.php
@@ -59,7 +59,7 @@ public function fields(): array
     }
 
     /** {@inheritdoc} */
-    public function inject(&$carrier, PropagationSetterInterface $setter = null, ContextInterface $context = null): void
+    public function inject(&$carrier, ?PropagationSetterInterface $setter = null, ?ContextInterface $context = null): void
     {
         $setter ??= ArrayAccessGetterSetter::getInstance();
         $context ??= Context::getCurrent();
@@ -81,7 +81,7 @@ public function inject(&$carrier, PropagationSetterInterface $setter = null, Con
     }
 
     /** {@inheritdoc} */
-    public function extract($carrier, PropagationGetterInterface $getter = null, ContextInterface $context = null): ContextInterface
+    public function extract($carrier, ?PropagationGetterInterface $getter = null, ?ContextInterface $context = null): ContextInterface
     {
         $getter ??= ArrayAccessGetterSetter::getInstance();
         $context ??= Context::getCurrent();
diff --git a/src/Context/Propagation/NoopTextMapPropagator.php b/src/Context/Propagation/NoopTextMapPropagator.php
index c408cfc79..62892b329 100644
--- a/src/Context/Propagation/NoopTextMapPropagator.php
+++ b/src/Context/Propagation/NoopTextMapPropagator.php
@@ -25,12 +25,12 @@ public function fields(): array
         return [];
     }
 
-    public function extract($carrier, PropagationGetterInterface $getter = null, ContextInterface $context = null): ContextInterface
+    public function extract($carrier, ?PropagationGetterInterface $getter = null, ?ContextInterface $context = null): ContextInterface
     {
         return $context ?? Context::getCurrent();
     }
 
-    public function inject(&$carrier, PropagationSetterInterface $setter = null, ContextInterface $context = null): void
+    public function inject(&$carrier, ?PropagationSetterInterface $setter = null, ?ContextInterface $context = null): void
     {
     }
 }
diff --git a/src/Context/Propagation/TextMapPropagatorInterface.php b/src/Context/Propagation/TextMapPropagatorInterface.php
index b2e6582fa..1be587452 100644
--- a/src/Context/Propagation/TextMapPropagatorInterface.php
+++ b/src/Context/Propagation/TextMapPropagatorInterface.php
@@ -26,7 +26,7 @@ public function fields() : array;
      *
      * @see https://github.com/open-telemetry/opentelemetry-specification/blob/v1.6.1/specification/context/api-propagators.md#textmap-inject
      */
-    public function inject(mixed &$carrier, PropagationSetterInterface $setter = null, ContextInterface $context = null): void;
+    public function inject(mixed &$carrier, ?PropagationSetterInterface $setter = null, ?ContextInterface $context = null): void;
 
     /**
      * Extracts specific values from the provided carrier into the provided {@see ContextInterface}
@@ -34,5 +34,5 @@ public function inject(mixed &$carrier, PropagationSetterInterface $setter = nul
      *
      * @see https://github.com/open-telemetry/opentelemetry-specification/blob/v1.6.1/specification/context/api-propagators.md#textmap-extract
      */
-    public function extract($carrier, PropagationGetterInterface $getter = null, ContextInterface $context = null): ContextInterface;
+    public function extract($carrier, ?PropagationGetterInterface $getter = null, ?ContextInterface $context = null): ContextInterface;
 }
diff --git a/src/SDK/Common/Configuration/Configuration.php b/src/SDK/Common/Configuration/Configuration.php
index 577c85708..e716f76ff 100644
--- a/src/SDK/Common/Configuration/Configuration.php
+++ b/src/SDK/Common/Configuration/Configuration.php
@@ -29,7 +29,7 @@ public static function has(string $name): bool
         return CompositeResolver::instance()->hasVariable($name);
     }
 
-    public static function getInt(string $key, int $default = null): int
+    public static function getInt(string $key, ?int $default = null): int
     {
         return (int) self::validateVariableValue(
             CompositeResolver::instance()->resolve(
@@ -40,7 +40,7 @@ public static function getInt(string $key, int $default = null): int
         );
     }
 
-    public static function getString(string $key, string $default = null): string
+    public static function getString(string $key, ?string $default = null): string
     {
         return (string) self::validateVariableValue(
             CompositeResolver::instance()->resolve(
@@ -50,7 +50,7 @@ public static function getString(string $key, string $default = null): string
         );
     }
 
-    public static function getBoolean(string $key, bool $default = null): bool
+    public static function getBoolean(string $key, ?bool $default = null): bool
     {
         $resolved = self::validateVariableValue(
             CompositeResolver::instance()->resolve(
@@ -78,7 +78,7 @@ public static function getMixed(string $key, $default = null)
         );
     }
 
-    public static function getMap(string $key, array $default = null): array
+    public static function getMap(string $key, ?array $default = null): array
     {
         return MapParser::parse(
             CompositeResolver::instance()->resolve(
@@ -88,7 +88,7 @@ public static function getMap(string $key, array $default = null): array
         );
     }
 
-    public static function getList(string $key, array $default = null): array
+    public static function getList(string $key, ?array $default = null): array
     {
         return ListParser::parse(
             CompositeResolver::instance()->resolve(
@@ -98,7 +98,7 @@ public static function getList(string $key, array $default = null): array
         );
     }
 
-    public static function getEnum(string $key, string $default = null): string
+    public static function getEnum(string $key, ?string $default = null): string
     {
         return (string) self::validateVariableValue(
             CompositeResolver::instance()->resolve(
@@ -108,7 +108,7 @@ public static function getEnum(string $key, string $default = null): string
         );
     }
 
-    public static function getFloat(string $key, float $default = null): float
+    public static function getFloat(string $key, ?float $default = null): float
     {
         return (float) self::validateVariableValue(
             CompositeResolver::instance()->resolve(
@@ -119,7 +119,7 @@ public static function getFloat(string $key, float $default = null): float
         );
     }
 
-    public static function getRatio(string $key, float $default = null): float
+    public static function getRatio(string $key, ?float $default = null): float
     {
         return RatioParser::parse(
             self::validateVariableValue(