diff --git a/src/Application.php b/src/Application.php
index 5fc89f7..4e15610 100644
--- a/src/Application.php
+++ b/src/Application.php
@@ -63,7 +63,7 @@ class Application
     /** @var callable The callable to catch exception, receives exception & exit code, may rethrow exception or may exit program */
     protected $onException = null;
 
-    public function __construct(protected string $name, protected string $version = '0.0.1', callable $onExit = null)
+    public function __construct(protected string $name, protected string $version = '0.0.1', ?callable $onExit = null)
     {
         $this->onExit = $onExit ?? static fn (int $exitCode = 0) => exit($exitCode);
 
@@ -115,7 +115,7 @@ public function argv(): array
      *
      * @return string|self
      */
-    public function logo(string $logo = null)
+    public function logo(?string $logo = null)
     {
         if (func_num_args() === 0) {
             return $this->logo;
@@ -247,7 +247,7 @@ public function commandFor(array $argv): Command
      *
      * @return Interactor|self
      */
-    public function io(Interactor $io = null)
+    public function io(?Interactor $io = null)
     {
         if ($io || !$this->io) {
             $this->io = $io ?? new Interactor;
diff --git a/src/Helper/Normalizer.php b/src/Helper/Normalizer.php
index 4c71c48..470114f 100644
--- a/src/Helper/Normalizer.php
+++ b/src/Helper/Normalizer.php
@@ -57,7 +57,7 @@ public function normalizeArgs(array $args): array
     /**
      * Normalizes value as per context and runs thorugh filter if possible.
      */
-    public function normalizeValue(Parameter $parameter, string $value = null): mixed
+    public function normalizeValue(Parameter $parameter, ?string $value = null): mixed
     {
         if ($parameter instanceof Option && $parameter->bool()) {
             return !$parameter->default();
diff --git a/src/Helper/OutputHelper.php b/src/Helper/OutputHelper.php
index 8685509..7cf9c5c 100644
--- a/src/Helper/OutputHelper.php
+++ b/src/Helper/OutputHelper.php
@@ -63,7 +63,7 @@ class OutputHelper
     /** @var int Max width of command name */
     protected int $maxCmdName = 0;
 
-    public function __construct(Writer $writer = null)
+    public function __construct(?Writer $writer = null)
     {
         $this->writer = $writer ?? new Writer;
     }
diff --git a/src/Helper/Shell.php b/src/Helper/Shell.php
index cb83d4c..3666d5d 100644
--- a/src/Helper/Shell.php
+++ b/src/Helper/Shell.php
@@ -188,9 +188,9 @@ protected function checkTimeout(): void
     // @codeCoverageIgnoreEnd
 
     public function setOptions(
-        string $cwd = null,
+        ?string $cwd = null,
         ?array $env = null,
-        float $timeout = null,
+        ?float $timeout = null,
         array $otherOptions = []
     ): self {
         $this->cwd            = $cwd;
diff --git a/src/IO/Interactor.php b/src/IO/Interactor.php
index 0971b1b..37c5a78 100644
--- a/src/IO/Interactor.php
+++ b/src/IO/Interactor.php
@@ -188,7 +188,7 @@ class Interactor
      * @param string|null $input  Input stream path.
      * @param string|null $output Output steam path.
      */
-    public function __construct(string $input = null, string $output = null)
+    public function __construct(?string $input = null, ?string $output = null)
     {
         $this->reader = new Reader($input);
         $this->writer = new Writer($output);
@@ -294,7 +294,7 @@ public function choices(string $text, array $choices, $default = null, bool $cas
      *
      * @return mixed
      */
-    public function prompt(string $text, $default = null, callable $fn = null, int $retry = 3): mixed
+    public function prompt(string $text, $default = null, ?callable $fn = null, int $retry = 3): mixed
     {
         $error  = 'Invalid value. Please try again!';
         $hidden = func_get_args()[4] ?? false;
@@ -328,7 +328,7 @@ public function prompt(string $text, $default = null, callable $fn = null, int $
      *
      * @return mixed
      */
-    public function promptHidden(string $text, callable $fn = null, int $retry = 3): mixed
+    public function promptHidden(string $text, ?callable $fn = null, int $retry = 3): mixed
     {
         return $this->prompt($text, null, $fn, $retry, true);
     }
diff --git a/src/Input/Command.php b/src/Input/Command.php
index 723ef76..5b999ee 100644
--- a/src/Input/Command.php
+++ b/src/Input/Command.php
@@ -145,7 +145,7 @@ public function app(): ?App
     /**
      * Bind command to the app.
      */
-    public function bind(App $app = null): self
+    public function bind(?App $app = null): self
     {
         $this->_app = $app;
 
@@ -189,7 +189,7 @@ public function argument(string $raw, string $desc = '', $default = null): self
     /**
      * Registers new option.
      */
-    public function option(string $raw, string $desc = '', callable $filter = null, $default = null): self
+    public function option(string $raw, string $desc = '', ?callable $filter = null, $default = null): self
     {
         $option = new Option($raw, $desc, $default, $filter);
 
@@ -217,7 +217,7 @@ public function userOptions(): array
      *
      * @return string|self
      */
-    public function usage(string $usage = null)
+    public function usage(?string $usage = null)
     {
         if (func_num_args() === 0) {
             return $this->_usage;
@@ -235,7 +235,7 @@ public function usage(string $usage = null)
      *
      * @return string|self
      */
-    public function alias(string $alias = null)
+    public function alias(?string $alias = null)
     {
         if (func_num_args() === 0) {
             return $this->_alias;
@@ -249,7 +249,7 @@ public function alias(string $alias = null)
     /**
      * Sets event handler for last (or given) option.
      */
-    public function on(callable $fn, string $option = null): self
+    public function on(callable $fn, ?string $option = null): self
     {
         $names = array_keys($this->allOptions());
 
@@ -271,7 +271,7 @@ public function onExit(callable $fn): self
     /**
      * {@inheritdoc}
      */
-    protected function handleUnknown(string $arg, string $value = null): mixed
+    protected function handleUnknown(string $arg, ?string $value = null): mixed
     {
         if ($this->_allowUnknown) {
             return $this->set($this->toCamelCase($arg), $value);
@@ -338,7 +338,7 @@ public function emit(string $event, $value = null): mixed
     /**
      * Tap return given object or if that is null then app instance. This aids for chaining.
      */
-    public function tap(object $object = null)
+    public function tap(?object $object = null)
     {
         return $object ?? $this->_app;
     }
@@ -358,7 +358,7 @@ public function interact(Interactor $io): void
      *
      * @return callable|self If $action provided then self, otherwise the preset action.
      */
-    public function action(callable $action = null)
+    public function action(?callable $action = null)
     {
         if (func_num_args() === 0) {
             return $this->_action;
@@ -388,7 +388,7 @@ protected function io(): Interactor
     /**
      * Get ProgressBar instance.
      */
-    protected function progress(int $total = null): ProgressBar
+    protected function progress(?int $total = null): ProgressBar
     {
         return new ProgressBar($total, $this->writer());
     }
diff --git a/src/Input/Parser.php b/src/Input/Parser.php
index 69a7876..42977ca 100644
--- a/src/Input/Parser.php
+++ b/src/Input/Parser.php
@@ -118,7 +118,7 @@ protected function parseArgs(string $arg)
      *
      * @return bool Whether to eat next arg.
      */
-    protected function parseOptions(string $arg, string $nextArg = null): bool
+    protected function parseOptions(string $arg, ?string $nextArg = null): bool
     {
         $value = substr($nextArg ?? '', 0, 1) === '-' ? null : $nextArg;
 
@@ -155,7 +155,7 @@ protected function optionFor(string $arg): ?Option
      *
      * @return mixed If true it will indicate that value has been eaten.
      */
-    abstract protected function handleUnknown(string $arg, string $value = null): mixed;
+    abstract protected function handleUnknown(string $arg, ?string $value = null): mixed;
 
     /**
      * Emit the event with value.
@@ -175,7 +175,7 @@ abstract protected function emit(string $event, $value = null): mixed;
      *
      * @return bool Indicating whether it has eaten adjoining arg to its right.
      */
-    protected function setValue(Parameter $parameter, string $value = null): bool
+    protected function setValue(Parameter $parameter, ?string $value = null): bool
     {
         $name  = $parameter->attributeName();
         $value = $this->_normalizer->normalizeValue($parameter, $value);
diff --git a/src/Input/Reader.php b/src/Input/Reader.php
index 1e2c008..9e0f907 100644
--- a/src/Input/Reader.php
+++ b/src/Input/Reader.php
@@ -42,7 +42,7 @@ class Reader
      *
      * @param string|null $path Read path. Defaults to STDIN.
      */
-    public function __construct(string $path = null)
+    public function __construct(?string $path = null)
     {
         $this->stream = $path ? fopen($path, 'r') : STDIN;
     }
@@ -55,7 +55,7 @@ public function __construct(string $path = null)
      *
      * @return mixed
      */
-    public function read($default = null, callable $fn = null): mixed
+    public function read($default = null, ?callable $fn = null): mixed
     {
         $in = rtrim(fgets($this->stream), "\r\n");
 
@@ -75,7 +75,7 @@ public function read($default = null, callable $fn = null): mixed
      *
      * @return string
      */
-    public function readAll(callable $fn = null): string
+    public function readAll(?callable $fn = null): string
     {
         $in = stream_get_contents($this->stream);
 
@@ -91,7 +91,7 @@ public function readAll(callable $fn = null): string
      *
      * @return string
      */
-    public function readPiped(callable $fn = null): string
+    public function readPiped(?callable $fn = null): string
     {
         $stdin = '';
         $read  = [$this->stream];
@@ -118,7 +118,7 @@ public function readPiped(callable $fn = null): string
      *
      * @return mixed
      */
-    public function readHidden($default = null, callable $fn = null): mixed
+    public function readHidden($default = null, ?callable $fn = null): mixed
     {
         // @codeCoverageIgnoreStart
         if ('\\' === DIRECTORY_SEPARATOR) {
@@ -144,7 +144,7 @@ public function readHidden($default = null, callable $fn = null): mixed
      *
      * @return mixed
      */
-    protected function readHiddenWinOS($default = null, callable $fn = null): mixed
+    protected function readHiddenWinOS($default = null, ?callable $fn = null): mixed
     {
         $cmd = 'powershell -Command ' . implode('; ', array_filter([
             '$pword = Read-Host -AsSecureString',
diff --git a/src/Output/ProgressBar.php b/src/Output/ProgressBar.php
index ff3e2d0..dcb4e27 100644
--- a/src/Output/ProgressBar.php
+++ b/src/Output/ProgressBar.php
@@ -202,7 +202,7 @@ public function forceRedraw(bool $force = true): self
      * @param iterable $items    Array or any other iterable object
      * @param callable $callback A handler to run on each item
      */
-    public function each($items, callable $callback = null)
+    public function each($items, ?callable $callback = null)
     {
         if ($items instanceof \Traversable) {
             $items = iterator_to_array($items);
diff --git a/src/Output/Writer.php b/src/Output/Writer.php
index aeda5d5..35bf90f 100644
--- a/src/Output/Writer.php
+++ b/src/Output/Writer.php
@@ -188,7 +188,7 @@ class Writer
 
     protected Terminal $terminal;
 
-    public function __construct(string $path = null, Color $colorizer = null)
+    public function __construct(?string $path = null, ?Color $colorizer = null)
     {
         if ($path) {
             $path = fopen($path, 'w');