diff --git a/phpstan.neon b/phpstan.neon
index 748bd9a..e078d5a 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -1,5 +1,5 @@
 parameters:
-    level: 7
+    level: 8
     paths:
         - src/
         - tests/
diff --git a/src/Auth/TokenSources/CLITokenSource.php b/src/Auth/TokenSources/CLITokenSource.php
index 1eba60e..3dd66fb 100644
--- a/src/Auth/TokenSources/CLITokenSource.php
+++ b/src/Auth/TokenSources/CLITokenSource.php
@@ -71,7 +71,7 @@ protected function parseFile(string $filename): void
     }
 
     /**
-     * @return array{project_name?: string, 'oauth_token': array{'accesstoken': string, 'expiresin': int, 'expiry': string, 'refreshtoken': string, 'tokentype': string}}
+     * @return array{project_name?: string, 'oauth_token': array{'accesstoken': string, 'expiresin': int, 'expiry': non-falsy-string|null, 'refreshtoken': string|null, 'tokentype': string}}
      */
     protected function toFile(): array
     {
@@ -80,7 +80,7 @@ protected function toFile(): array
             'oauth_token' => [
                 'accesstoken' => $this->accessToken,
                 'expiresin' => $this->expiresIn,
-                'expiry' => $this->expiry->format(DATE_RFC3339_EXTENDED),
+                'expiry' => $this->expiry?->format(DATE_RFC3339_EXTENDED),
                 'refreshtoken' => $this->refreshToken,
                 'tokentype' => $this->tokenType,
             ],
diff --git a/src/Compute/Models/Machine.php b/src/Compute/Models/Machine.php
index 968854b..9f79753 100644
--- a/src/Compute/Models/Machine.php
+++ b/src/Compute/Models/Machine.php
@@ -141,6 +141,8 @@ public function updatedFields(): array
      */
     public function stop(StopMachineRequest $request = new StopMachineRequest()): Operation
     {
+        assert($this->client !== null);
+
         return $this->client->stop($this->getID(), $request);
     }
 
@@ -151,6 +153,8 @@ public function stop(StopMachineRequest $request = new StopMachineRequest()): Op
      */
     public function start(StartMachineRequest $request = new StartMachineRequest()): Operation
     {
+        assert($this->client !== null);
+
         return $this->client->start($this->getID(), $request);
     }
 
@@ -161,6 +165,8 @@ public function start(StartMachineRequest $request = new StartMachineRequest()):
      */
     public function reset(ResetMachineRequest $request = new ResetMachineRequest()): Operation
     {
+        assert($this->client !== null);
+
         return $this->client->reset($this->getID(), $request);
     }
 
@@ -171,6 +177,8 @@ public function reset(ResetMachineRequest $request = new ResetMachineRequest()):
      */
     public function delete(DeleteMachineRequest $request = new DeleteMachineRequest()): Operation
     {
+        assert($this->client !== null);
+
         return $this->client->delete($this->getID(), $request);
     }
 
diff --git a/tests/Integration/Compute/MachinesTest.php b/tests/Integration/Compute/MachinesTest.php
index 0c0d3d8..0955f01 100644
--- a/tests/Integration/Compute/MachinesTest.php
+++ b/tests/Integration/Compute/MachinesTest.php
@@ -48,18 +48,21 @@ protected function tearDown(): void
 
     public function test_list_machines(): void
     {
+        assert($this->client !== null);
         $response = $this->client->machines()->list();
         self::assertGreaterThan(0, count($response->getMachines()), 'Expected at least one machine');
     }
 
     public function test_get_machine(): void
     {
+        assert($this->client !== null);
         $machine = $this->client->machines()->get('php-cbws-test1');
         self::assertEquals('zones/nl-ein-1/types/g2.1', $machine->getType(), 'Expected machine to have g2.1 type');
     }
 
     public function test_stop_machine(): void
     {
+        assert($this->client !== null);
         $machine = $this->client->machines()->get('php-cbws-test1');
         $operation = $machine->stop()->await();
 
@@ -71,6 +74,7 @@ public function test_stop_machine(): void
 
     public function test_start_machine(): void
     {
+        assert($this->client !== null);
         $machine = $this->client->machines()->get('php-cbws-test1');
         $operation = $machine->start()->await();