diff --git a/composer.json b/composer.json
index 63b4f03..d08cc94 100644
--- a/composer.json
+++ b/composer.json
@@ -68,8 +68,8 @@
         "lint": "parallel-lint src tests",
         "phpcs": "phpcs src tests --standard=psr2 -sp --colors",
         "phpstan": [
-            "phpstan analyse -c phpstan.neon src --level 2 --no-progress",
-            "phpstan analyse -c phpstan-tests.neon tests --level 2 --no-progress"
+            "phpstan analyse -c phpstan.neon src --level max --no-progress",
+            "phpstan analyse -c phpstan-tests.neon tests --level 5 --no-progress"
         ],
         "phpunit": "phpunit --verbose --colors=always",
         "phpunit-coverage": "phpunit --verbose --colors=always --coverage-html build/coverage",
diff --git a/phpstan.neon b/phpstan.neon
index e574e17..24bd048 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -1,3 +1,17 @@
 parameters:
+    checkMissingIterableValueType: false
     autoload_files:
         - tests/phpstan-bootstrap.php
+    ignoreErrors:
+        -
+            message: "#^Negated boolean expression is always false\\.$#"
+            count: 1
+            path: src/Uuid.php
+        -
+            message: '#^Comparison operation "<" between int<6, max> and 0 is always false\.$#'
+            count: 1
+            path: src/Generator/CombGenerator.php
+        -
+            message: '#^Comparison operation ">" between 6 and 0 is always true\.$#'
+            count: 1
+            path: src/Generator/CombGenerator.php
diff --git a/src/Codec/GuidStringCodec.php b/src/Codec/GuidStringCodec.php
index 3675480..a4c1d77 100644
--- a/src/Codec/GuidStringCodec.php
+++ b/src/Codec/GuidStringCodec.php
@@ -53,7 +53,7 @@ class GuidStringCodec extends StringCodec
     {
         $components = array_values($uuid->getFieldsHex());
 
-        return hex2bin(implode('', $components));
+        return (string) hex2bin(implode('', $components));
     }
 
     /**
diff --git a/src/Codec/OrderedTimeCodec.php b/src/Codec/OrderedTimeCodec.php
index de91aab..7f05d64 100644
--- a/src/Codec/OrderedTimeCodec.php
+++ b/src/Codec/OrderedTimeCodec.php
@@ -42,7 +42,7 @@ class OrderedTimeCodec extends StringCodec
             $fields['node'],
         ];
 
-        return hex2bin(implode('', $optimized));
+        return (string) hex2bin(implode('', $optimized));
     }
 
     /**
diff --git a/src/Codec/StringCodec.php b/src/Codec/StringCodec.php
index f1bc024..1735088 100644
--- a/src/Codec/StringCodec.php
+++ b/src/Codec/StringCodec.php
@@ -66,7 +66,7 @@ class StringCodec implements CodecInterface
      */
     public function encodeBinary(UuidInterface $uuid)
     {
-        return hex2bin($uuid->getHex());
+        return (string) hex2bin($uuid->getHex());
     }
 
     /**
diff --git a/src/Codec/TimestampFirstCombCodec.php b/src/Codec/TimestampFirstCombCodec.php
index 9d13af7..a630369 100644
--- a/src/Codec/TimestampFirstCombCodec.php
+++ b/src/Codec/TimestampFirstCombCodec.php
@@ -52,7 +52,7 @@ class TimestampFirstCombCodec extends StringCodec
     {
         $stringEncoding = $this->encode($uuid);
 
-        return hex2bin(str_replace('-', '', $stringEncoding));
+        return (string) hex2bin(str_replace('-', '', $stringEncoding));
     }
 
     /**
diff --git a/src/Converter/Number/DegradedNumberConverter.php b/src/Converter/Number/DegradedNumberConverter.php
index 96a011c..b219ce6 100644
--- a/src/Converter/Number/DegradedNumberConverter.php
+++ b/src/Converter/Number/DegradedNumberConverter.php
@@ -28,7 +28,7 @@ class DegradedNumberConverter implements NumberConverterInterface
      * Throws an `UnsatisfiedDependencyException`
      *
      * @param string $hex The hexadecimal string representation to convert
-     * @return void
+     * @return mixed
      * @throws UnsatisfiedDependencyException
      */
     public function fromHex($hex)
@@ -44,7 +44,7 @@ class DegradedNumberConverter implements NumberConverterInterface
      * Throws an `UnsatisfiedDependencyException`
      *
      * @param mixed $integer An integer representation to convert
-     * @return void
+     * @return string
      * @throws UnsatisfiedDependencyException
      */
     public function toHex($integer)
diff --git a/src/Converter/Time/DegradedTimeConverter.php b/src/Converter/Time/DegradedTimeConverter.php
index b94589c..3e05dd8 100644
--- a/src/Converter/Time/DegradedTimeConverter.php
+++ b/src/Converter/Time/DegradedTimeConverter.php
@@ -29,7 +29,7 @@ class DegradedTimeConverter implements TimeConverterInterface
      *
      * @param string $seconds
      * @param string $microSeconds
-     * @return void
+     * @return string[]
      * @throws UnsatisfiedDependencyException if called on a 32-bit system and `Moontoast\Math\BigNumber` is not present
      */
     public function calculateTime($seconds, $microSeconds)
diff --git a/src/DegradedUuid.php b/src/DegradedUuid.php
index 2669761..87fb46a 100644
--- a/src/DegradedUuid.php
+++ b/src/DegradedUuid.php
@@ -50,6 +50,7 @@ class DegradedUuid extends Uuid
      * For degraded UUIDs, throws an `UnsatisfiedDependencyException` when
      * called on a 32-bit system
      *
+     * @return array
      * @throws UnsatisfiedDependencyException if called on a 32-bit system
      */
     public function getFields()
@@ -65,6 +66,7 @@ class DegradedUuid extends Uuid
      * For degraded UUIDs, throws an `UnsatisfiedDependencyException` when
      * called on a 32-bit system
      *
+     * @return int
      * @throws UnsatisfiedDependencyException if called on a 32-bit system
      */
     public function getNode()
@@ -81,6 +83,7 @@ class DegradedUuid extends Uuid
      * For degraded UUIDs, throws an `UnsatisfiedDependencyException` when
      * called on a 32-bit system
      *
+     * @return int
      * @throws UnsatisfiedDependencyException if called on a 32-bit system
      */
     public function getTimeLow()
@@ -97,6 +100,7 @@ class DegradedUuid extends Uuid
      * For degraded UUIDs, throws an `UnsatisfiedDependencyException` when
      * called on a 32-bit system
      *
+     * @return int
      * @throws UnsatisfiedDependencyException if called on a 32-bit system
      * @throws UnsupportedOperationException If this UUID is not a version 1 UUID
      */
diff --git a/src/FeatureSet.php b/src/FeatureSet.php
index e2203d0..f74a71d 100644
--- a/src/FeatureSet.php
+++ b/src/FeatureSet.php
@@ -193,6 +193,7 @@ class FeatureSet
      * Sets the time provider for use in this environment
      *
      * @param TimeProviderInterface $timeProvider
+     * @return void
      */
     public function setTimeProvider(TimeProviderInterface $timeProvider)
     {
diff --git a/src/Generator/CombGenerator.php b/src/Generator/CombGenerator.php
index 1d4a5f6..9a9387d 100644
--- a/src/Generator/CombGenerator.php
+++ b/src/Generator/CombGenerator.php
@@ -74,7 +74,7 @@ class CombGenerator implements RandomGeneratorInterface
 
         $lsbTime = str_pad($this->converter->toHex($this->timestamp()), self::TIMESTAMP_BYTES * 2, '0', STR_PAD_LEFT);
 
-        return hex2bin(str_pad(bin2hex($hash), $length - self::TIMESTAMP_BYTES, '0') . $lsbTime);
+        return (string) hex2bin(str_pad(bin2hex($hash), $length - self::TIMESTAMP_BYTES, '0') . $lsbTime);
     }
 
     /**
diff --git a/src/Generator/DefaultTimeGenerator.php b/src/Generator/DefaultTimeGenerator.php
index 5c5ccb2..13a063e 100644
--- a/src/Generator/DefaultTimeGenerator.php
+++ b/src/Generator/DefaultTimeGenerator.php
@@ -92,7 +92,7 @@ class DefaultTimeGenerator implements TimeGeneratorInterface
         // Create a 60-bit time value as a count of 100-nanosecond intervals
         // since 00:00:00.00, 15 October 1582
         $timeOfDay = $this->timeProvider->currentTime();
-        $uuidTime = $this->timeConverter->calculateTime($timeOfDay['sec'], $timeOfDay['usec']);
+        $uuidTime = $this->timeConverter->calculateTime((string) $timeOfDay['sec'], (string) $timeOfDay['usec']);
 
         $timeHi = BinaryUtils::applyVersion($uuidTime['hi'], 1);
         $clockSeqHi = BinaryUtils::applyVariant($clockSeq >> 8);
@@ -109,14 +109,14 @@ class DefaultTimeGenerator implements TimeGeneratorInterface
             ]
         );
 
-        return hex2bin($hex);
+        return (string) hex2bin($hex);
     }
 
     /**
      * Uses the node provider given when constructing this instance to get
      * the node ID (usually a MAC address)
      *
-     * @param string|int $node A node value that may be used to override the node provider
+     * @param string|int|null $node A node value that may be used to override the node provider
      * @return string Hexadecimal representation of the node ID
      * @throws InvalidArgumentException
      * @throws Exception
diff --git a/src/Generator/OpenSslGenerator.php b/src/Generator/OpenSslGenerator.php
index 47abf9b..ba95297 100644
--- a/src/Generator/OpenSslGenerator.php
+++ b/src/Generator/OpenSslGenerator.php
@@ -38,6 +38,6 @@ class OpenSslGenerator implements RandomGeneratorInterface
      */
     public function generate($length)
     {
-        return openssl_random_pseudo_bytes($length);
+        return (string) openssl_random_pseudo_bytes($length);
     }
 }
diff --git a/src/Generator/RandomLibAdapter.php b/src/Generator/RandomLibAdapter.php
index 5aa0e88..a6c2fab 100644
--- a/src/Generator/RandomLibAdapter.php
+++ b/src/Generator/RandomLibAdapter.php
@@ -40,13 +40,13 @@ class RandomLibAdapter implements RandomGeneratorInterface
      */
     public function __construct(Generator $generator = null)
     {
-        $this->generator = $generator;
-
-        if ($this->generator === null) {
+        if ($generator === null) {
             $factory = new Factory();
 
-            $this->generator = $factory->getHighStrengthGenerator();
+            $generator = $factory->getHighStrengthGenerator();
         }
+
+        $this->generator = $generator;
     }
 
     /**
diff --git a/src/Provider/Node/FallbackNodeProvider.php b/src/Provider/Node/FallbackNodeProvider.php
index 83488ab..a30aaec 100644
--- a/src/Provider/Node/FallbackNodeProvider.php
+++ b/src/Provider/Node/FallbackNodeProvider.php
@@ -43,7 +43,7 @@ class FallbackNodeProvider implements NodeProviderInterface
      * Returns the system node ID by iterating over an array of node providers
      * and returning the first non-empty value found
      *
-     * @return string System node ID as a hexadecimal string
+     * @return string|null System node ID as a hexadecimal string
      * @throws Exception
      */
     public function getNode()
diff --git a/src/Provider/Node/SystemNodeProvider.php b/src/Provider/Node/SystemNodeProvider.php
index 5701513..892cbba 100644
--- a/src/Provider/Node/SystemNodeProvider.php
+++ b/src/Provider/Node/SystemNodeProvider.php
@@ -38,19 +38,25 @@ class SystemNodeProvider implements NodeProviderInterface
         $pattern = '/[^:]([0-9A-Fa-f]{2}([:-])[0-9A-Fa-f]{2}(\2[0-9A-Fa-f]{2}){4})[^:]/';
         $matches = [];
 
-        // first try a  linux specific way
+        // first try a linux specific way
         $node = $this->getSysfs();
 
         // Search the ifconfig output for all MAC addresses and return
         // the first one found
         if ($node === false) {
             if (preg_match_all($pattern, $this->getIfconfig(), $matches, PREG_PATTERN_ORDER)) {
-                $node = $matches[1][0];
+                $node = $matches[1][0] ?? false;
             }
         }
+
         if ($node !== false) {
             $node = str_replace([':', '-'], '', $node);
+
+            if (is_array($node)) {
+                $node = $node[0] ?? false;
+            }
         }
+
         return $node;
     }
 
@@ -62,7 +68,7 @@ class SystemNodeProvider implements NodeProviderInterface
      */
     protected function getIfconfig()
     {
-        if (strpos(strtolower(ini_get('disable_functions')), 'passthru') !== false) {
+        if (strpos(strtolower((string) ini_get('disable_functions')), 'passthru') !== false) {
             return '';
         }
 
@@ -83,7 +89,7 @@ class SystemNodeProvider implements NodeProviderInterface
                 break;
         }
 
-        return ob_get_clean();
+        return (string) ob_get_clean();
     }
 
     /**
@@ -112,12 +118,13 @@ class SystemNodeProvider implements NodeProviderInterface
             $macs = array_map('trim', $macs);
 
             // remove invalid entries
-            $macs = array_filter($macs, function ($mac) {
-                return
+            $macs = array_filter($macs, function ($address) {
+                return (
                     // localhost adapter
-                    $mac !== '00:00:00:00:00:00' &&
-                    // must match  mac adress
-                    preg_match('/^([0-9a-f]{2}:){5}[0-9a-f]{2}$/i', $mac);
+                    $address !== '00:00:00:00:00:00'
+                    // must match mac address
+                    && preg_match('/^([0-9a-f]{2}:){5}[0-9a-f]{2}$/i', $address)
+                );
             });
 
             $mac = reset($macs);
diff --git a/src/Provider/Time/FixedTimeProvider.php b/src/Provider/Time/FixedTimeProvider.php
index 02b36d7..6fafe70 100644
--- a/src/Provider/Time/FixedTimeProvider.php
+++ b/src/Provider/Time/FixedTimeProvider.php
@@ -49,6 +49,7 @@ class FixedTimeProvider implements TimeProviderInterface
      * Sets the `usec` component of the timestamp
      *
      * @param int $value The `usec` value to set
+     * @return void
      */
     public function setUsec($value)
     {
@@ -59,6 +60,7 @@ class FixedTimeProvider implements TimeProviderInterface
      * Sets the `sec` component of the timestamp
      *
      * @param int $value The `sec` value to set
+     * @return void
      */
     public function setSec($value)
     {
diff --git a/src/Uuid.php b/src/Uuid.php
index 6c6d597..58699b8 100644
--- a/src/Uuid.php
+++ b/src/Uuid.php
@@ -233,8 +233,9 @@ class Uuid implements UuidInterface
      * Re-constructs the object from its serialized form.
      *
      * @param string $serialized
-     * @link http://php.net/manual/en/class.serializable.php
+     * @return void
      * @throws InvalidUuidStringException
+     * @link http://php.net/manual/en/class.serializable.php
      */
     public function unserialize($serialized)
     {
@@ -288,7 +289,7 @@ class Uuid implements UuidInterface
      */
     public function getClockSeqHiAndReserved()
     {
-        return hexdec($this->getClockSeqHiAndReservedHex());
+        return (int) hexdec($this->getClockSeqHiAndReservedHex());
     }
 
     public function getClockSeqHiAndReservedHex()
@@ -303,7 +304,7 @@ class Uuid implements UuidInterface
      */
     public function getClockSeqLow()
     {
-        return hexdec($this->getClockSeqLowHex());
+        return (int) hexdec($this->getClockSeqLowHex());
     }
 
     public function getClockSeqLowHex()
@@ -473,7 +474,7 @@ class Uuid implements UuidInterface
      */
     public function getNode()
     {
-        return hexdec($this->getNodeHex());
+        return (int) hexdec($this->getNodeHex());
     }
 
     public function getNodeHex()
@@ -489,7 +490,7 @@ class Uuid implements UuidInterface
      */
     public function getTimeHiAndVersion()
     {
-        return hexdec($this->getTimeHiAndVersionHex());
+        return (int) hexdec($this->getTimeHiAndVersionHex());
     }
 
     public function getTimeHiAndVersionHex()
@@ -504,7 +505,7 @@ class Uuid implements UuidInterface
      */
     public function getTimeLow()
     {
-        return hexdec($this->getTimeLowHex());
+        return (int) hexdec($this->getTimeLowHex());
     }
 
     public function getTimeLowHex()
@@ -519,7 +520,7 @@ class Uuid implements UuidInterface
      */
     public function getTimeMid()
     {
-        return hexdec($this->getTimeMidHex());
+        return (int) hexdec($this->getTimeMidHex());
     }
 
     public function getTimeMidHex()
@@ -549,7 +550,7 @@ class Uuid implements UuidInterface
             throw new UnsupportedOperationException('Not a time-based UUID');
         }
 
-        return hexdec($this->getTimestampHex());
+        return (int) hexdec($this->getTimestampHex());
     }
 
     /**
@@ -625,6 +626,7 @@ class Uuid implements UuidInterface
      * Sets the factory used to create UUIDs.
      *
      * @param UuidFactoryInterface $factory
+     * @return void
      */
     public static function setFactory(UuidFactoryInterface $factory)
     {
diff --git a/src/UuidFactory.php b/src/UuidFactory.php
index 5a57b09..0436f6f 100644
--- a/src/UuidFactory.php
+++ b/src/UuidFactory.php
@@ -85,6 +85,7 @@ class UuidFactory implements UuidFactoryInterface
      * Sets the UUID coder-decoder used by this factory
      *
      * @param CodecInterface $codec
+     * @return void
      */
     public function setCodec(CodecInterface $codec)
     {
@@ -125,6 +126,7 @@ class UuidFactory implements UuidFactoryInterface
      * Sets the time-based UUID generator this factory will use to generate version 1 UUIDs
      *
      * @param TimeGeneratorInterface $generator
+     * @return void
      */
     public function setTimeGenerator(TimeGeneratorInterface $generator)
     {
@@ -145,6 +147,7 @@ class UuidFactory implements UuidFactoryInterface
      * Sets the random UUID generator this factory will use to generate version 4 UUIDs
      *
      * @param RandomGeneratorInterface $generator
+     * @return void
      */
     public function setRandomGenerator(RandomGeneratorInterface $generator)
     {
@@ -155,6 +158,7 @@ class UuidFactory implements UuidFactoryInterface
      * Sets the number converter this factory will use
      *
      * @param NumberConverterInterface $converter
+     * @return void
      */
     public function setNumberConverter(NumberConverterInterface $converter)
     {
@@ -175,6 +179,7 @@ class UuidFactory implements UuidFactoryInterface
      * Sets the UUID builder this factory will use when creating `Uuid` instances
      *
      * @param UuidBuilderInterface $builder
+     * @return void
      */
     public function setUuidBuilder(UuidBuilderInterface $builder)
     {
@@ -272,7 +277,7 @@ class UuidFactory implements UuidFactoryInterface
      * @param string|UuidInterface $ns The UUID namespace to use
      * @param string $name The string to hash together with the namespace
      * @param int $version The version of UUID to create (3 or 5)
-     * @param string $hashFunction The hash function to use when hashing together
+     * @param callable $hashFunction The hash function to use when hashing together
      *     the namespace and name
      * @return UuidInterface
      * @throws InvalidUuidStringException
@@ -299,7 +304,7 @@ class UuidFactory implements UuidFactoryInterface
     protected function uuidFromHashedName($hash, $version)
     {
         $timeHi = BinaryUtils::applyVersion(substr($hash, 12, 4), $version);
-        $clockSeqHi = BinaryUtils::applyVariant(hexdec(substr($hash, 16, 2)));
+        $clockSeqHi = BinaryUtils::applyVariant((int) hexdec(substr($hash, 16, 2)));
 
         $fields = [
             'time_low' => substr($hash, 0, 8),
diff --git a/tests/Codec/GuidStringCodecTest.php b/tests/Codec/GuidStringCodecTest.php
index 3488ead..dd6b087 100644
--- a/tests/Codec/GuidStringCodecTest.php
+++ b/tests/Codec/GuidStringCodecTest.php
@@ -40,9 +40,7 @@ class GuidStringCodecTest extends TestCase
     protected function tearDown(): void
     {
         parent::tearDown();
-        $this->builder = null;
-        $this->fields = null;
-        $this->uuid = null;
+        unset($this->builder, $this->fields, $this->uuid);
     }
 
     public function testEncodeUsesFieldsArray()
diff --git a/tests/Codec/OrderedTimeCodecTest.php b/tests/Codec/OrderedTimeCodecTest.php
index b2c178d..b2c1a2e 100644
--- a/tests/Codec/OrderedTimeCodecTest.php
+++ b/tests/Codec/OrderedTimeCodecTest.php
@@ -47,9 +47,7 @@ class OrderedTimeCodecTest extends TestCase
     protected function tearDown(): void
     {
         parent::tearDown();
-        $this->builder = null;
-        $this->uuid = null;
-        $this->fields = null;
+        unset($this->builder, $this->uuid, $this->fields);
     }
 
     public function testEncodeUsesFieldsArray()
diff --git a/tests/Codec/StringCodecTest.php b/tests/Codec/StringCodecTest.php
index b00220f..0309a14 100644
--- a/tests/Codec/StringCodecTest.php
+++ b/tests/Codec/StringCodecTest.php
@@ -44,9 +44,7 @@ class StringCodecTest extends TestCase
     protected function tearDown(): void
     {
         parent::tearDown();
-        $this->builder = null;
-        $this->uuid = null;
-        $this->fields = null;
+        unset($this->builder, $this->uuid, $this->fields);
     }
 
     public function testEncodeUsesFieldsArray()
diff --git a/tests/Converter/Time/PhpTimeConverterTest.php b/tests/Converter/Time/PhpTimeConverterTest.php
index 0fe25a5..d96b182 100644
--- a/tests/Converter/Time/PhpTimeConverterTest.php
+++ b/tests/Converter/Time/PhpTimeConverterTest.php
@@ -25,7 +25,7 @@ class PhpTimeConverterTest extends TestCase
         ];
 
         $converter = new PhpTimeConverter();
-        $returned = $converter->calculateTime($seconds, $microSeconds);
+        $returned = $converter->calculateTime((string) $seconds, (string) $microSeconds);
         $this->assertEquals($expectedArray, $returned);
     }
 }
diff --git a/tests/Generator/DefaultTimeGeneratorTest.php b/tests/Generator/DefaultTimeGeneratorTest.php
index 598011c..802d53f 100644
--- a/tests/Generator/DefaultTimeGeneratorTest.php
+++ b/tests/Generator/DefaultTimeGeneratorTest.php
@@ -48,9 +48,7 @@ class DefaultTimeGeneratorTest extends TestCase
     protected function tearDown(): void
     {
         parent::tearDown();
-        $this->timeProvider = null;
-        $this->nodeProvider = null;
-        $this->timeConverter = null;
+        unset($this->timeProvider, $this->nodeProvider, $this->timeConverter);
         Mockery::close();
         AspectMock::clean();
     }
diff --git a/tests/Provider/Time/FixedTimeProviderTest.php b/tests/Provider/Time/FixedTimeProviderTest.php
index 35b38d5..b4d6468 100644
--- a/tests/Provider/Time/FixedTimeProviderTest.php
+++ b/tests/Provider/Time/FixedTimeProviderTest.php
@@ -26,7 +26,7 @@ class FixedTimeProviderTest extends TestCase
         $timestamp = ['sec' => 1458844556, 'usec' => 200997];
         $provider = new FixedTimeProvider($timestamp);
 
-        $newTimestamp = ['sec' => 1050804050, 'usec' => '30192'];
+        $newTimestamp = ['sec' => 1050804050, 'usec' => 30192];
         $provider->setSec($newTimestamp['sec']);
         $provider->setUsec($newTimestamp['usec']);
 
diff --git a/tests/UuidTest.php b/tests/UuidTest.php
index b875de2..448e529 100644
--- a/tests/UuidTest.php
+++ b/tests/UuidTest.php
@@ -650,12 +650,12 @@ class UuidTest extends TestCase
         // Check with a recent date
         $uuid = Uuid::fromString('ff6f8cb0-c57d-11e1-9b21-0800200c9a66');
         $this->assertEquals('ff6f8cb0-c57d-11e1-9b21-0800200c9a66', $uuid->toString());
-        $this->assertEquals('ff6f8cb0-c57d-11e1-9b21-0800200c9a66', sprintf('%s', $uuid));
+        $this->assertEquals('ff6f8cb0-c57d-11e1-9b21-0800200c9a66', sprintf('%s', (string) $uuid));
 
         // Check with an old date
         $uuid = Uuid::fromString('0901e600-0154-1000-9b21-0800200c9a66');
         $this->assertEquals('0901e600-0154-1000-9b21-0800200c9a66', $uuid->toString());
-        $this->assertEquals('0901e600-0154-1000-9b21-0800200c9a66', sprintf('%s', $uuid));
+        $this->assertEquals('0901e600-0154-1000-9b21-0800200c9a66', sprintf('%s', (string) $uuid));
     }
 
     /**
@@ -746,7 +746,7 @@ class UuidTest extends TestCase
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('Invalid node value');
 
-        $uuid = Uuid::uuid1(9223372036854775808);
+        $uuid = Uuid::uuid1('9223372036854775808');
     }
 
     public function testUuid1WithNonHexadecimalNode()
@@ -1034,7 +1034,6 @@ class UuidTest extends TestCase
 
         $this->assertTrue($uuid1->equals($uuid2));
         $this->assertFalse($uuid1->equals($uuid3));
-        $this->assertFalse($uuid1->equals(null));
         $this->assertFalse($uuid1->equals(new stdClass()));
     }
 
@@ -1942,20 +1941,6 @@ class UuidTest extends TestCase
         $this->assertEquals('4ae71336-e44b-39bf-b9d2-752e234818a5', $uuid->toString());
     }
 
-    public function testUuid3WithNullName()
-    {
-        $uuid = Uuid::uuid3(Uuid::NIL, null);
-
-        $this->assertEquals('4ae71336-e44b-39bf-b9d2-752e234818a5', $uuid->toString());
-    }
-
-    public function testUuid3WithFalseName()
-    {
-        $uuid = Uuid::uuid3(Uuid::NIL, false);
-
-        $this->assertEquals('4ae71336-e44b-39bf-b9d2-752e234818a5', $uuid->toString());
-    }
-
     public function testUuid3WithZeroName()
     {
         $uuid = Uuid::uuid3(Uuid::NIL, '0');
@@ -1978,20 +1963,6 @@ class UuidTest extends TestCase
         $this->assertEquals('e129f27c-5103-5c5c-844b-cdf0a15e160d', $uuid->toString());
     }
 
-    public function testUuid5WithNullName()
-    {
-        $uuid = Uuid::uuid5(Uuid::NIL, null);
-
-        $this->assertEquals('e129f27c-5103-5c5c-844b-cdf0a15e160d', $uuid->toString());
-    }
-
-    public function testUuid5WithFalseName()
-    {
-        $uuid = Uuid::uuid5(Uuid::NIL, false);
-
-        $this->assertEquals('e129f27c-5103-5c5c-844b-cdf0a15e160d', $uuid->toString());
-    }
-
     public function testUuid5WithZeroName()
     {
         $uuid = Uuid::uuid5(Uuid::NIL, '0');