diff --git a/phpstan.neon b/phpstan.neon
index 9110ad71..f5dcb9ed 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -4,7 +4,7 @@ parameters:
         - tests
     parallel:
         maximumNumberOfProcesses: 4
-    level: 6
+    level: 7
     inferPrivatePropertyTypeFromConstructor: true
     bootstrapFiles:
       - tools/bootstrap.php
diff --git a/src/Parameters/CreateMeetingParameters.php b/src/Parameters/CreateMeetingParameters.php
index 85ace07d..8350efc8 100644
--- a/src/Parameters/CreateMeetingParameters.php
+++ b/src/Parameters/CreateMeetingParameters.php
@@ -363,7 +363,7 @@ public function getPresentations(): array
         return $this->presentations;
     }
 
-    public function getPresentationsAsXML(): string|false
+    public function getPresentationsAsXML(): string
     {
         $result = '';
 
@@ -389,6 +389,10 @@ public function getPresentationsAsXML(): string|false
             $result = $xml->asXML();
         }
 
+        if (false === $result) {
+            throw new \LogicException('Could not generate XML.');
+        }
+
         return $result;
     }
 
diff --git a/src/Parameters/InsertDocumentParameters.php b/src/Parameters/InsertDocumentParameters.php
index 538266e6..aee8ad32 100644
--- a/src/Parameters/InsertDocumentParameters.php
+++ b/src/Parameters/InsertDocumentParameters.php
@@ -52,7 +52,7 @@ public function removePresentation(string $url): self
         return $this;
     }
 
-    public function getPresentationsAsXML(): string|false
+    public function getPresentationsAsXML(): string
     {
         $result = '';
 
@@ -77,6 +77,10 @@ public function getPresentationsAsXML(): string|false
             $result = $xml->asXML();
         }
 
+        if (false === $result) {
+            throw new \LogicException('Could not generate XML.');
+        }
+
         return $result;
     }
 }
diff --git a/tests/unit/Parameters/CreateMeetingParametersTest.php b/tests/unit/Parameters/CreateMeetingParametersTest.php
index a9389a61..2f2adc25 100644
--- a/tests/unit/Parameters/CreateMeetingParametersTest.php
+++ b/tests/unit/Parameters/CreateMeetingParametersTest.php
@@ -216,7 +216,13 @@ public function testGetPresentationsAsXMLWithFile(): void
     {
         $params = $this->generateCreateParams();
         $createMeetingParams = $this->getCreateMock($params);
-        $createMeetingParams->addPresentation('bbb_logo.png', file_get_contents(__DIR__.\DIRECTORY_SEPARATOR.'..'.\DIRECTORY_SEPARATOR.'..'.\DIRECTORY_SEPARATOR.'fixtures'.\DIRECTORY_SEPARATOR.'bbb_logo.png'));
+
+        $content = file_get_contents(
+            __DIR__ . \DIRECTORY_SEPARATOR . '..' . \DIRECTORY_SEPARATOR . '..' . \DIRECTORY_SEPARATOR . 'fixtures' . \DIRECTORY_SEPARATOR . 'bbb_logo.png'
+        );
+        $this->assertIsString($content);
+
+        $createMeetingParams->addPresentation('bbb_logo.png', $content);
         $this->assertXmlStringEqualsXmlFile(__DIR__.\DIRECTORY_SEPARATOR.'..'.\DIRECTORY_SEPARATOR.'..'.\DIRECTORY_SEPARATOR.'fixtures'.\DIRECTORY_SEPARATOR.'presentation_with_embedded_file.xml', $createMeetingParams->getPresentationsAsXML());
     }
 
diff --git a/tests/unit/Responses/GetMeetingsResponseTest.php b/tests/unit/Responses/GetMeetingsResponseTest.php
index f39df44a..d9d506a9 100644
--- a/tests/unit/Responses/GetMeetingsResponseTest.php
+++ b/tests/unit/Responses/GetMeetingsResponseTest.php
@@ -85,12 +85,16 @@ public function testGetMeetingsNoMeetings(): void
     {
         // scalelite response no meetings
         $xml = simplexml_load_string('<response><returncode>SUCCESS</returncode><messageKey>noMeetings</messageKey><message>No meetings were found on this server.</message></response>');
+        $this->assertInstanceOf(\SimpleXMLElement::class, $xml);
+
         $this->meetings = new GetMeetingsResponse($xml);
         $this->assertEquals('SUCCESS', $this->meetings->getReturnCode());
         $this->assertCount(0, $this->meetings->getMeetings());
 
         // normal bbb response no meetings
         $xml = simplexml_load_string('<response><returncode>SUCCESS</returncode><meetings/><messageKey>noMeetings</messageKey><message>No meetings were found on this server.</message></response>');
+        $this->assertInstanceOf(\SimpleXMLElement::class, $xml);
+
         $this->meetings = new GetMeetingsResponse($xml);
         $this->assertEquals('SUCCESS', $this->meetings->getReturnCode());
         $this->assertCount(0, $this->meetings->getMeetings());
diff --git a/tests/unit/Responses/GetRecordingsResponseTest.php b/tests/unit/Responses/GetRecordingsResponseTest.php
index d95d8e6b..38bc372a 100644
--- a/tests/unit/Responses/GetRecordingsResponseTest.php
+++ b/tests/unit/Responses/GetRecordingsResponseTest.php
@@ -128,7 +128,10 @@ public function testHasNoRecordings(): void
           <message>There are no recordings for the meeting(s).</message>
         </response>';
 
-        $response = new GetRecordingsResponse(simplexml_load_string($xml));
+        $xml = simplexml_load_string($xml);
+        $this->assertInstanceOf(\SimpleXMLElement::class, $xml);
+
+        $response = new GetRecordingsResponse($xml);
 
         $this->assertTrue($response->hasNoRecordings());
     }
diff --git a/tests/unit/Responses/HooksDestroyResponseTest.php b/tests/unit/Responses/HooksDestroyResponseTest.php
index 7704ee1a..4838e7cf 100644
--- a/tests/unit/Responses/HooksDestroyResponseTest.php
+++ b/tests/unit/Responses/HooksDestroyResponseTest.php
@@ -53,6 +53,7 @@ public function testHooksDestroyResponseTypes(): void
     public function testHookDestroyMissingHook(): void
     {
         $xml = simplexml_load_string('<response><returncode>FAILED</returncode><messageKey>destroyMissingHook</messageKey><message>The hook informed was not found.</message></response>');
+        $this->assertInstanceOf(\SimpleXMLElement::class, $xml);
 
         $destroyResponse = new HooksDestroyResponse($xml);
         $this->assertTrue($destroyResponse->failed());
@@ -62,6 +63,7 @@ public function testHookDestroyMissingHook(): void
     public function testHookDestroyHookError(): void
     {
         $xml = simplexml_load_string('<response><returncode>FAILED</returncode><messageKey>destroyHookError</messageKey><message>An error happened while removing your hook. Check the logs.</message></response>');
+        $this->assertInstanceOf(\SimpleXMLElement::class, $xml);
 
         $destroyResponse = new HooksDestroyResponse($xml);
         $this->assertTrue($destroyResponse->failed());
diff --git a/tests/unit/Responses/InsertDocumentResponseTest.php b/tests/unit/Responses/InsertDocumentResponseTest.php
index 01d1012e..62899ad6 100644
--- a/tests/unit/Responses/InsertDocumentResponseTest.php
+++ b/tests/unit/Responses/InsertDocumentResponseTest.php
@@ -41,7 +41,12 @@ public function testIsMeetingRunningResponseContent(): void
     {
         $this->assertEquals('SUCCESS', $this->running->getReturnCode());
 
-        $this->assertEquals('<?xmlversion="1.0"?><response><returncode>SUCCESS</returncode></response>', $this->minifyString($this->running->getRawXml()->asXML()));
+        $xml = $this->running->getRawXml()->asXML();
+        $this->assertIsString($xml);
+
+        $this->assertEquals('<?xmlversion="1.0"?><response><returncode>SUCCESS</returncode></response>', $this->minifyString(
+            $xml
+        ));
     }
 
     public function testIsMeetingRunningResponseTypes(): void
diff --git a/tests/unit/Responses/IsMeetingRunningResponseTest.php b/tests/unit/Responses/IsMeetingRunningResponseTest.php
index 70dce13f..003cf7f2 100644
--- a/tests/unit/Responses/IsMeetingRunningResponseTest.php
+++ b/tests/unit/Responses/IsMeetingRunningResponseTest.php
@@ -43,7 +43,12 @@ public function testIsMeetingRunningResponseContent(): void
         $this->assertEquals('SUCCESS', $this->running->getReturnCode());
         $this->assertTrue($this->running->isRunning());
 
-        $this->assertEquals('<?xmlversion="1.0"?><response><returncode>SUCCESS</returncode><running>true</running></response>', $this->minifyString($this->running->getRawXml()->asXML()));
+        $xml = $this->running->getRawXml()->asXML();
+        $this->assertIsString($xml);
+
+        $this->assertEquals('<?xmlversion="1.0"?><response><returncode>SUCCESS</returncode><running>true</running></response>', $this->minifyString(
+            $xml
+        ));
     }
 
     public function testIsMeetingRunningResponseTypes(): void
diff --git a/tests/unit/Util/ArrayHelperTest.php b/tests/unit/Util/ArrayHelperTest.php
index 9ea33908..2e0cc9e7 100644
--- a/tests/unit/Util/ArrayHelperTest.php
+++ b/tests/unit/Util/ArrayHelperTest.php
@@ -29,7 +29,7 @@
  */
 final class ArrayHelperTest extends TestCase
 {
-    /** @return iterable<string,array<string|array-key,string|bool>> */
+    /** @return iterable<array<mixed>> */
     public function provideArrays(): iterable
     {
         yield 'simple flat arrays' => [