diff --git a/.gitattributes b/.gitattributes
index 65a00ff..2abe789 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,10 +1,12 @@
 # exclude dev files from export to reduce archive download size
 /.gitattributes export-ignore
+/.github/ISSUE_TEMPLATE/ export-ignore
 /.github/workflows/ export-ignore
 /.gitignore export-ignore
 /docs/ export-ignore
 /examples/ export-ignore
 /mkdocs.yml export-ignore
+/phpstan.neon.dist export-ignore
 /phpunit.xml.dist export-ignore
 /phpunit.xml.legacy export-ignore
 /tests/ export-ignore
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f7ef07a..4b63994 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -34,6 +34,28 @@ jobs:
       - run: vendor/bin/phpunit --coverage-text --stderr -c phpunit.xml.legacy
         if: ${{ matrix.php < 7.3 }}
 
+  PHPStan:
+    name: PHPStan (PHP ${{ matrix.php }})
+    runs-on: ubuntu-22.04
+    strategy:
+      matrix:
+        php:
+          - 8.2
+          - 8.1
+          - 8.0
+          - 7.4
+          - 7.3
+          - 7.2
+          - 7.1
+    steps:
+      - uses: actions/checkout@v3
+      - uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          coverage: none
+      - run: composer install
+      - run: vendor/bin/phpstan
+
   Built-in-webserver:
     name: Built-in webserver (PHP ${{ matrix.php }})
     runs-on: ubuntu-22.04
diff --git a/composer.json b/composer.json
index b914d81..aa590bd 100644
--- a/composer.json
+++ b/composer.json
@@ -18,6 +18,7 @@
         "react/promise": "^3 || ^2.7"
     },
     "require-dev": {
+        "phpstan/phpstan": "1.8.10 || 1.4.10",
         "phpunit/phpunit": "^9.5 || ^7.5",
         "psr/container": "^2 || ^1"
     },
diff --git a/examples/index.php b/examples/index.php
index 3ae7e74..5bf34f7 100644
--- a/examples/index.php
+++ b/examples/index.php
@@ -118,7 +118,7 @@
    return new React\Http\Message\Response(
         React\Http\Message\Response::STATUS_OK,
         [
-            'Content-Length' => 5,
+            'Content-Length' => '5',
             'Content-Type' => 'text/plain; charset=utf-8',
             'X-Is-Head' => 'true'
         ]
@@ -161,7 +161,7 @@
             React\Http\Message\Response::STATUS_NOT_MODIFIED,
             [
                 'ETag' => $etag,
-                'Content-Length' => strlen($etag) - 1
+                'Content-Length' => (string) (strlen($etag) - 1)
             ]
         );
     }
@@ -193,7 +193,7 @@
 $app->get('/error/yield', function () {
     yield null;
 });
-$app->get('/error/class', 'Acme\Http\UnknownDeleteUserController');
+$app->get('/error/class', 'Acme\Http\UnknownDeleteUserController'); // @phpstan-ignore-line
 
 // OPTIONS *
 $app->options('', function () {
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
new file mode 100644
index 0000000..428e5d0
--- /dev/null
+++ b/phpstan.neon.dist
@@ -0,0 +1,17 @@
+parameters:
+    level: 5
+
+    paths:
+        - examples/
+        - src/
+        - tests/
+
+    reportUnmatchedIgnoredErrors: false
+    ignoreErrors:
+        # ignore generic usage like `PromiseInterface<ResponseInterface>` until fixed upstream
+        - '/^PHPDoc tag @return contains generic type React\\Promise\\PromiseInterface<Psr\\Http\\Message\\ResponseInterface> but interface React\\Promise\\PromiseInterface is not generic\.$/'
+        # ignore unknown `Fiber` class (PHP 8.1+)
+        - '/^Instantiated class Fiber not found\.$/'
+        - '/^Call to method (start|isTerminated|getReturn)\(\) on an unknown class Fiber\.$/'
+        # ignore incomplete type information for mocks in legacy PHPUnit 7.5
+        - '/^Parameter #\d+ \$.+ of class .+ constructor expects .+, PHPUnit\\Framework\\MockObject\\MockObject given\.$/'
diff --git a/src/App.php b/src/App.php
index cd4b16c..30d93ad 100644
--- a/src/App.php
+++ b/src/App.php
@@ -286,7 +286,7 @@ private function runLoop()
         } while (true);
 
         // remove signal handlers when loop stops (if registered)
-        Loop::removeSignal(\defined('SIGINT') ? \SIGINT : 2, $f1);
+        Loop::removeSignal(\defined('SIGINT') ? \SIGINT : 2, $f1 ?? 'printf');
         Loop::removeSignal(\defined('SIGTERM') ? \SIGTERM : 15, $f2 ?? 'printf');
     }
 
@@ -309,11 +309,12 @@ private function runOnce()
 
     /**
      * @param ServerRequestInterface $request
-     * @return ResponseInterface|PromiseInterface<ResponseInterface,void>
+     * @return ResponseInterface|PromiseInterface<ResponseInterface>
      *     Returns a response or a Promise which eventually fulfills with a
      *     response. This method never throws or resolves a rejected promise.
      *     If the request can not be routed or the handler fails, it will be
      *     turned into a valid error response before returning.
+     * @throws void
      */
     private function handleRequest(ServerRequestInterface $request)
     {
diff --git a/src/Container.php b/src/Container.php
index 7c4521b..def505b 100644
--- a/src/Container.php
+++ b/src/Container.php
@@ -13,9 +13,10 @@ class Container
     /** @var array<string,object|callable():(object|scalar|null)|scalar|null>|ContainerInterface */
     private $container;
 
-    /** @var array<string,callable():(object|scalar|null) | object | scalar | null>|ContainerInterface $loader */
+    /** @param array<string,callable():(object|scalar|null) | object | scalar | null>|ContainerInterface $loader */
     public function __construct($loader = [])
     {
+        /** @var mixed $loader explicit type check for mixed if user ignores parameter type */
         if (!\is_array($loader) && !$loader instanceof ContainerInterface) {
             throw new \TypeError(
                 'Argument #1 ($loader) must be of type array|Psr\Container\ContainerInterface, ' . (\is_object($loader) ? get_class($loader) : gettype($loader)) . ' given'
@@ -233,6 +234,7 @@ private function loadParameter(\ReflectionParameter $parameter, int $depth, bool
         $hasDefault = $parameter->isDefaultValueAvailable() || ((!$type instanceof \ReflectionNamedType || $type->getName() !== 'mixed') && $parameter->allowsNull());
 
         // abort for union types (PHP 8.0+) and intersection types (PHP 8.1+)
+        // @phpstan-ignore-next-line for PHP < 8
         if ($type instanceof \ReflectionUnionType || $type instanceof \ReflectionIntersectionType) { // @codeCoverageIgnoreStart
             if ($hasDefault) {
                 return $parameter->isDefaultValueAvailable() ? $parameter->getDefaultValue() : null;
diff --git a/src/ErrorHandler.php b/src/ErrorHandler.php
index b70f53c..e2feebe 100644
--- a/src/ErrorHandler.php
+++ b/src/ErrorHandler.php
@@ -22,7 +22,7 @@ public function __construct()
     }
 
     /**
-     * @return ResponseInterface|PromiseInterface<ResponseInterface,void>|\Generator
+     * @return ResponseInterface|PromiseInterface<ResponseInterface>|\Generator
      *     Returns a response, a Promise which eventually fulfills with a
      *     response or a Generator which eventually returns a response. This
      *     method never throws or resolves a rejected promise. If the next
diff --git a/src/Io/FiberHandler.php b/src/Io/FiberHandler.php
index a9deff0..e23107d 100644
--- a/src/Io/FiberHandler.php
+++ b/src/Io/FiberHandler.php
@@ -21,7 +21,7 @@
 class FiberHandler
 {
     /**
-     * @return ResponseInterface|PromiseInterface<ResponseInterface,void>|\Generator
+     * @return ResponseInterface|PromiseInterface<ResponseInterface>|\Generator
      *     Returns a `ResponseInterface` from the next request handler in the
      *     chain. If the next request handler returns immediately, this method
      *     will return immediately. If the next request handler suspends the
@@ -42,6 +42,9 @@ public function __invoke(ServerRequestInterface $request, callable $next): mixed
             $response = $next($request);
             assert($response instanceof ResponseInterface || $response instanceof PromiseInterface || $response instanceof \Generator);
 
+            // if the next request handler returns immediately, the fiber can terminate immediately without using a Deferred
+            // if the next request handler suspends the fiber, we only reach this point after resuming the fiber, so the code below will have assigned a Deferred
+            /** @var ?Deferred $deferred */
             if ($deferred !== null) {
                 $deferred->resolve($response);
             }
@@ -49,8 +52,10 @@ public function __invoke(ServerRequestInterface $request, callable $next): mixed
             return $response;
         });
 
+        /** @throws void because the next handler will always be an `ErrorHandler` */
         $fiber->start();
         if ($fiber->isTerminated()) {
+            /** @throws void because fiber is known to have terminated successfully */
             return $fiber->getReturn();
         }
 
diff --git a/src/Io/RouteHandler.php b/src/Io/RouteHandler.php
index 5757d05..2d637e3 100644
--- a/src/Io/RouteHandler.php
+++ b/src/Io/RouteHandler.php
@@ -76,7 +76,7 @@ public function map(array $methods, string $route, $handler, ...$handlers): void
     public function __invoke(ServerRequestInterface $request)
     {
         if ($request->getRequestTarget()[0] !== '/' && $request->getRequestTarget() !== '*') {
-            return $this->errorHandler->requestProxyUnsupported($request);
+            return $this->errorHandler->requestProxyUnsupported();
         }
 
         if ($this->routeDispatcher === null) {
@@ -84,20 +84,29 @@ public function __invoke(ServerRequestInterface $request)
         }
 
         $routeInfo = $this->routeDispatcher->dispatch($request->getMethod(), $request->getUri()->getPath());
-        switch ($routeInfo[0]) {
-            case \FastRoute\Dispatcher::NOT_FOUND:
-                return $this->errorHandler->requestNotFound($request);
-            case \FastRoute\Dispatcher::METHOD_NOT_ALLOWED:
-                return $this->errorHandler->requestMethodNotAllowed($routeInfo[1]);
-            case \FastRoute\Dispatcher::FOUND:
-                $handler = $routeInfo[1];
-                $vars = $routeInfo[2];
-
-                foreach ($vars as $key => $value) {
-                    $request = $request->withAttribute($key, rawurldecode($value));
-                }
-
-                return $handler($request);
+        assert(\is_array($routeInfo) && isset($routeInfo[0]));
+
+        // happy path: matching route found, assign route attributes and invoke request handler
+        if ($routeInfo[0] === \FastRoute\Dispatcher::FOUND) {
+            $handler = $routeInfo[1];
+            $vars = $routeInfo[2];
+
+            foreach ($vars as $key => $value) {
+                $request = $request->withAttribute($key, rawurldecode($value));
+            }
+
+            return $handler($request);
         }
-    } // @codeCoverageIgnore
+
+        // no matching route found: report error `404 Not Found`
+        if ($routeInfo[0] === \FastRoute\Dispatcher::NOT_FOUND) {
+            return $this->errorHandler->requestNotFound();
+        }
+
+        // unexpected request method for route: report error `405 Method Not Allowed`
+        assert($routeInfo[0] === \FastRoute\Dispatcher::METHOD_NOT_ALLOWED);
+        assert(\is_array($routeInfo[1]) && \count($routeInfo[1]) > 0);
+
+        return $this->errorHandler->requestMethodNotAllowed($routeInfo[1]);
+    }
 }
diff --git a/src/Io/SapiHandler.php b/src/Io/SapiHandler.php
index e3baeab..37218dd 100644
--- a/src/Io/SapiHandler.php
+++ b/src/Io/SapiHandler.php
@@ -46,7 +46,7 @@ public function requestFromGlobals(): ServerRequestInterface
         $target = ($_SERVER['REQUEST_URI'] ?? '/');
         $url = $target;
         if (($target[0] ?? '/') === '/' || $target === '*') {
-            $url = ($_SERVER['HTTPS'] ?? null === 'on' ? 'https://' : 'http://') . ($host ?? 'localhost') . ($target === '*' ? '' : $target);
+            $url = (($_SERVER['HTTPS'] ?? null) === 'on' ? 'https://' : 'http://') . ($host ?? 'localhost') . ($target === '*' ? '' : $target);
         }
 
         $body = file_get_contents('php://input');
diff --git a/tests/AccessLogHandlerTest.php b/tests/AccessLogHandlerTest.php
index d4037ea..db38244 100644
--- a/tests/AccessLogHandlerTest.php
+++ b/tests/AccessLogHandlerTest.php
@@ -143,7 +143,7 @@ public function testInvokeWithCoroutineNextPrintsRequestLogWithCurrentDateAndTim
         $response = new Response(200, [], "Hello\n");
 
         $generator = $handler($request, function () use ($response) {
-            if (false) {
+            if (false) { // @phpstan-ignore-line
                 yield;
             }
             return $response;
diff --git a/tests/AppTest.php b/tests/AppTest.php
index 468f041..24c9947 100644
--- a/tests/AppTest.php
+++ b/tests/AppTest.php
@@ -1230,7 +1230,7 @@ public function testHandleRequestWithMatchingRouteReturnsResponseWhenHandlerRetu
         $app = $this->createAppWithoutLogger();
 
         $app->get('/users', function () {
-            if (false) {
+            if (false) { // @phpstan-ignore-line
                 yield;
             }
 
@@ -1611,7 +1611,7 @@ public function testHandleRequestWithMatchingRouteReturnsInternalServerErrorResp
 
         $line = __LINE__ + 5;
         $app->get('/users', function () {
-            if (false) {
+            if (false) { // @phpstan-ignore-line
                 yield;
             }
             throw new \RuntimeException('Foo');
@@ -1837,7 +1837,7 @@ public function testHandleRequestWithMatchingRouteReturnsInternalServerErrorResp
     {
         $app = $this->createAppWithoutLogger();
 
-        $app->get('/users', 'UnknownClass');
+        $app->get('/users', 'UnknownClass'); // @phpstan-ignore-line
 
         $request = new ServerRequest('GET', 'http://localhost/users');
 
diff --git a/tests/ContainerTest.php b/tests/ContainerTest.php
index 5c5ea8b..0c09c6d 100644
--- a/tests/ContainerTest.php
+++ b/tests/ContainerTest.php
@@ -134,10 +134,11 @@ public function testCallableReturnsCallableForUnionWithNullViaAutowiringWillDefa
     {
         $request = new ServerRequest('GET', 'http://example.com/');
 
+        // @phpstan-ignore-next-line for PHP < 8
         $controller = new class(null) {
             private $data = false;
 
-            #[PHP8] public function __construct(string|int|null $data) { $this->data = $data; }
+            #[PHP8] public function __construct(string|int|null $data) { $this->data = $data; } // @phpstan-ignore-line
 
             public function __invoke(ServerRequestInterface $request)
             {
@@ -223,10 +224,11 @@ public function testCallableReturnsCallableForUnionWithIntDefaultValueViaAutowir
     {
         $request = new ServerRequest('GET', 'http://example.com/');
 
+        // @phpstan-ignore-next-line for PHP < 8
         $controller = new class(null) {
             private $data = false;
 
-            #[PHP8] public function __construct(string|int|null $data = 42) { $this->data = $data; }
+            #[PHP8] public function __construct(string|int|null $data = 42) { $this->data = $data; } // @phpstan-ignore-line
 
             public function __invoke(ServerRequestInterface $request)
             {
@@ -281,10 +283,11 @@ public function testCallableReturnsCallableForMixedWithStringDefaultViaAutowirin
     {
         $request = new ServerRequest('GET', 'http://example.com/');
 
+        // @phpstan-ignore-next-line for PHP < 8
         $controller = new class(null) {
             private $data = false;
 
-            #[PHP8] public function __construct(mixed $data = 'empty') { $this->data = $data; }
+            #[PHP8] public function __construct(mixed $data = 'empty') { $this->data = $data; } // @phpstan-ignore-line
 
             public function __invoke(ServerRequestInterface $request)
             {
@@ -773,7 +776,8 @@ public function __invoke()
             }
         };
 
-        $fn = #[PHP8] fn(mixed $data = 42) => new Response(200, [], json_encode($data));
+        $fn = null;
+        $fn = #[PHP8] fn(mixed $data = 42) => new Response(200, [], json_encode($data)); // @phpstan-ignore-line
         $container = new Container([
             ResponseInterface::class => $fn,
             'data' => null
@@ -844,7 +848,7 @@ public function __invoke()
             ResponseInterface::class => function (?\stdClass $user, ?\stdClass $data) {
                 return new Response(200, [], json_encode(['user' => $user, 'data' => $data]));
             },
-            'user' => function (): ?\stdClass {
+            'user' => function (): ?\stdClass { // @phpstan-ignore-line
                 return (object) [];
             }
         ]);
@@ -1717,7 +1721,7 @@ public function testCtorThrowsWhenMapContainsInvalidArray()
         $this->expectException(\BadMethodCallException::class);
         $this->expectExceptionMessage('Map for all contains unexpected array');
 
-        new Container([
+        new Container([ // @phpstan-ignore-line
             'all' => []
         ]);
     }
@@ -1944,7 +1948,7 @@ public function testCallableReturnsCallableThatThrowsWhenFactoryReturnsInvalidCl
 
         $container = new Container($psr);
 
-        $callable = $container->callable('FooBar');
+        $callable = $container->callable('FooBar'); // @phpstan-ignore-line
 
         $this->expectException(\BadMethodCallException::class);
         $this->expectExceptionMessage('Request handler class FooBar failed to load: Unable to load class');
@@ -2175,6 +2179,6 @@ public function testCtorWithInvalidValueThrows()
     {
         $this->expectException(\TypeError::class);
         $this->expectExceptionMessage('Argument #1 ($loader) must be of type array|Psr\Container\ContainerInterface, stdClass given');
-        new Container((object) []);
+        new Container((object) []); // @phpstan-ignore-line
     }
 }
diff --git a/tests/ErrorHandlerTest.php b/tests/ErrorHandlerTest.php
index a90c366..d565a52 100644
--- a/tests/ErrorHandlerTest.php
+++ b/tests/ErrorHandlerTest.php
@@ -53,7 +53,7 @@ public function testInvokeWithHandlerReturningGeneratorReturningResponseReturnsG
         $response = new Response();
 
         $generator = $handler($request, function () use ($response) {
-            if (false) {
+            if (false) { // @phpstan-ignore-line
                 yield;
             }
             return $response;
@@ -166,7 +166,7 @@ public function testInvokeWithHandlerReturningGeneratorThrowingExceptionReturnsG
         $request = new ServerRequest('GET', 'http://example.com/');
 
         $generator = $handler($request, function () {
-            if (false) {
+            if (false) { // @phpstan-ignore-line
                 yield;
             }
             throw new \RuntimeException();
@@ -324,7 +324,7 @@ public function testInvokeWithHandlerReturningGeneratorReturningNullReturnsGener
         $request = new ServerRequest('GET', 'http://example.com/');
 
         $generator = $handler($request, function () {
-            if (false) {
+            if (false) { // @phpstan-ignore-line
                 yield;
             }
             return null;
diff --git a/tests/Fixtures/InvalidConstructorInt.php b/tests/Fixtures/InvalidConstructorInt.php
index d5b62c2..d8d2f2f 100644
--- a/tests/Fixtures/InvalidConstructorInt.php
+++ b/tests/Fixtures/InvalidConstructorInt.php
@@ -6,5 +6,6 @@ class InvalidConstructorInt
 {
     public function __construct(int $value)
     {
+        assert(is_int($value));
     }
 }
diff --git a/tests/Fixtures/InvalidConstructorIntersection.php b/tests/Fixtures/InvalidConstructorIntersection.php
index ddbd84a..7431cbd 100644
--- a/tests/Fixtures/InvalidConstructorIntersection.php
+++ b/tests/Fixtures/InvalidConstructorIntersection.php
@@ -5,7 +5,6 @@
 /** PHP 8.1+ **/
 class InvalidConstructorIntersection
 {
-    public function __construct(\Traversable&\ArrayAccess $value)
-    {
-    }
+    // @phpstan-ignore-next-line for PHP < 8
+    #[PHP8] public function __construct(\Traversable&\ArrayAccess $value) { assert($value instanceof \Traversable && $value instanceof \ArrayAccess); }
 }
diff --git a/tests/Fixtures/InvalidConstructorSelf.php b/tests/Fixtures/InvalidConstructorSelf.php
index 74d81d1..a242d44 100644
--- a/tests/Fixtures/InvalidConstructorSelf.php
+++ b/tests/Fixtures/InvalidConstructorSelf.php
@@ -6,5 +6,6 @@ class InvalidConstructorSelf
 {
     public function __construct(InvalidConstructorSelf $value)
     {
+        assert($value instanceof self);
     }
 }
diff --git a/tests/Fixtures/InvalidConstructorUnion.php b/tests/Fixtures/InvalidConstructorUnion.php
index ea96ce1..49d0c08 100644
--- a/tests/Fixtures/InvalidConstructorUnion.php
+++ b/tests/Fixtures/InvalidConstructorUnion.php
@@ -5,7 +5,6 @@
 /** PHP 8.0+ **/
 class InvalidConstructorUnion
 {
-    public function __construct(int|float $value)
-    {
-    }
+    // @phpstan-ignore-next-line for PHP < 8
+    #[PHP8] public function __construct(int|float $value) { assert(is_int($value) || is_float($value)); }
 }
diff --git a/tests/Fixtures/InvalidConstructorUnknown.php b/tests/Fixtures/InvalidConstructorUnknown.php
index 47005b2..a89a577 100644
--- a/tests/Fixtures/InvalidConstructorUnknown.php
+++ b/tests/Fixtures/InvalidConstructorUnknown.php
@@ -4,7 +4,7 @@
 
 class InvalidConstructorUnknown
 {
-    public function __construct(\UnknownClass $value)
+    public function __construct(\UnknownClass $value) // @phpstan-ignore-line
     {
     }
 }
diff --git a/tests/Fixtures/InvalidConstructorUntyped.php b/tests/Fixtures/InvalidConstructorUntyped.php
index f0d10ac..ae95d17 100644
--- a/tests/Fixtures/InvalidConstructorUntyped.php
+++ b/tests/Fixtures/InvalidConstructorUntyped.php
@@ -4,7 +4,9 @@
 
 class InvalidConstructorUntyped
 {
+    /** @param mixed $value */
     public function __construct($value)
     {
+        assert($value === $value);
     }
 }
diff --git a/tests/Io/FiberHandlerTest.php b/tests/Io/FiberHandlerTest.php
index 26837a2..ac1e781 100644
--- a/tests/Io/FiberHandlerTest.php
+++ b/tests/Io/FiberHandlerTest.php
@@ -61,7 +61,7 @@ public function testInvokeWithHandlerReturningGeneratorReturningResponseReturnsG
         $response = new Response();
 
         $generator = $handler($request, function () use ($response) {
-            if (false) {
+            if (false) { // @phpstan-ignore-line
                 yield;
             }
             return $response;
diff --git a/tests/Io/RouteHandlerTest.php b/tests/Io/RouteHandlerTest.php
index ae5f0fa..b38a81b 100644
--- a/tests/Io/RouteHandlerTest.php
+++ b/tests/Io/RouteHandlerTest.php
@@ -200,6 +200,7 @@ public function testHandleRequestWithGetRequestReturnsResponseFromMatchingHandle
         $controller = new class {
             public static $response;
             public function __construct(int $value = null) {
+                assert($value === null);
             }
             public function __invoke() {
                 return self::$response;
@@ -223,6 +224,7 @@ public function testHandleRequestWithGetRequestReturnsResponseFromMatchingHandle
         $controller = new class(null) {
             public static $response;
             public function __construct(?int $value) {
+                assert($value === null);
             }
             public function __invoke() {
                 return self::$response;
diff --git a/tests/Io/SapiHandlerTest.php b/tests/Io/SapiHandlerTest.php
index 277b95d..17758a9 100644
--- a/tests/Io/SapiHandlerTest.php
+++ b/tests/Io/SapiHandlerTest.php
@@ -216,7 +216,7 @@ public function testSendResponseSendsEmptyBodyWithGivenHeadersButWithoutExplicit
 
         $_SERVER['SERVER_PROTOCOL'] = 'http/1.1';
         $sapi = new SapiHandler();
-        $response = new Response(204, ['Content-Type' => 'application/json', 'Content-Length' => 2], '{}');
+        $response = new Response(204, ['Content-Type' => 'application/json', 'Content-Length' => '2'], '{}');
 
         $this->expectOutputString('');
         $sapi->sendResponse($response);