diff --git a/.php-cs-fixer.php b/.php-cs-fixer.php
index 85f56fea..c860c516 100644
--- a/.php-cs-fixer.php
+++ b/.php-cs-fixer.php
@@ -25,6 +25,8 @@
         'ordered_imports' => true,
         'phpdoc_summary' => false,
         'protected_to_private' => false,
+        'get_class_to_class_keyword' => false, // override for PHP < 8.0 (because ::class usage is not allowed there)
+        'modernize_strpos' => false, // override for PHP < 8.0 (because str_contains not available in PHP 7.x)
     ])
 ;
 
diff --git a/src/Smalot/PdfParser/Document.php b/src/Smalot/PdfParser/Document.php
index 9c6835c0..f6a90abd 100644
--- a/src/Smalot/PdfParser/Document.php
+++ b/src/Smalot/PdfParser/Document.php
@@ -59,12 +59,12 @@ class Document
     /**
      * @var Header
      */
-    protected $trailer = null;
+    protected $trailer;
 
     /**
      * @var array
      */
-    protected $details = null;
+    protected $details;
 
     public function __construct()
     {
@@ -182,12 +182,12 @@ public function getObjectById(string $id)
         return null;
     }
 
-    public function hasObjectsByType(string $type, ?string $subtype = null): bool
+    public function hasObjectsByType(string $type, string $subtype = null): bool
     {
         return 0 < \count($this->getObjectsByType($type, $subtype));
     }
 
-    public function getObjectsByType(string $type, ?string $subtype = null): array
+    public function getObjectsByType(string $type, string $subtype = null): array
     {
         if (!isset($this->dictionary[$type])) {
             return [];
@@ -264,7 +264,7 @@ public function getPages()
         throw new \Exception('Missing catalog.');
     }
 
-    public function getText(?int $pageLimit = null): string
+    public function getText(int $pageLimit = null): string
     {
         $texts = [];
         $pages = $this->getPages();
diff --git a/src/Smalot/PdfParser/Element.php b/src/Smalot/PdfParser/Element.php
index bdd4afc3..df61c583 100644
--- a/src/Smalot/PdfParser/Element.php
+++ b/src/Smalot/PdfParser/Element.php
@@ -51,11 +51,11 @@ class Element
     /**
      * @var Document
      */
-    protected $document = null;
+    protected $document;
 
-    protected $value = null;
+    protected $value;
 
-    public function __construct($value, ?Document $document = null)
+    public function __construct($value, Document $document = null)
     {
         $this->value = $value;
         $this->document = $document;
@@ -96,7 +96,7 @@ public function __toString(): string
         return (string) $this->value;
     }
 
-    public static function parse(string $content, ?Document $document = null, int &$position = 0)
+    public static function parse(string $content, Document $document = null, int &$position = 0)
     {
         $args = \func_get_args();
         $only_values = isset($args[3]) ? $args[3] : false;
diff --git a/src/Smalot/PdfParser/Element/ElementArray.php b/src/Smalot/PdfParser/Element/ElementArray.php
index b54bf843..6ad22204 100644
--- a/src/Smalot/PdfParser/Element/ElementArray.php
+++ b/src/Smalot/PdfParser/Element/ElementArray.php
@@ -42,7 +42,7 @@
  */
 class ElementArray extends Element
 {
-    public function __construct($value, ?Document $document = null)
+    public function __construct($value, Document $document = null)
     {
         parent::__construct($value, $document);
     }
@@ -107,7 +107,7 @@ protected function resolveXRef(string $name)
      *
      * @return bool|ElementArray
      */
-    public static function parse(string $content, ?Document $document = null, int &$offset = 0)
+    public static function parse(string $content, Document $document = null, int &$offset = 0)
     {
         if (preg_match('/^\s*\[(?P<array>.*)/is', $content, $match)) {
             preg_match_all('/(.*?)(\[|\])/s', trim($content), $matches);
diff --git a/src/Smalot/PdfParser/Element/ElementBoolean.php b/src/Smalot/PdfParser/Element/ElementBoolean.php
index 55fb4638..4831a4ab 100644
--- a/src/Smalot/PdfParser/Element/ElementBoolean.php
+++ b/src/Smalot/PdfParser/Element/ElementBoolean.php
@@ -61,7 +61,7 @@ public function equals($value): bool
     /**
      * @return bool|ElementBoolean
      */
-    public static function parse(string $content, ?Document $document = null, int &$offset = 0)
+    public static function parse(string $content, Document $document = null, int &$offset = 0)
     {
         if (preg_match('/^\s*(?P<value>true|false)/is', $content, $match)) {
             $value = $match['value'];
diff --git a/src/Smalot/PdfParser/Element/ElementDate.php b/src/Smalot/PdfParser/Element/ElementDate.php
index 5f3d29f4..c4d39840 100644
--- a/src/Smalot/PdfParser/Element/ElementDate.php
+++ b/src/Smalot/PdfParser/Element/ElementDate.php
@@ -98,7 +98,7 @@ public function __toString(): string
     /**
      * @return bool|ElementDate
      */
-    public static function parse(string $content, ?Document $document = null, int &$offset = 0)
+    public static function parse(string $content, Document $document = null, int &$offset = 0)
     {
         if (preg_match('/^\s*\(D\:(?P<name>.*?)\)/s', $content, $match)) {
             $name = $match['name'];
diff --git a/src/Smalot/PdfParser/Element/ElementHexa.php b/src/Smalot/PdfParser/Element/ElementHexa.php
index e3265d23..d0314618 100644
--- a/src/Smalot/PdfParser/Element/ElementHexa.php
+++ b/src/Smalot/PdfParser/Element/ElementHexa.php
@@ -42,7 +42,7 @@ class ElementHexa extends ElementString
     /**
      * @return bool|ElementHexa|ElementDate
      */
-    public static function parse(string $content, ?Document $document = null, int &$offset = 0)
+    public static function parse(string $content, Document $document = null, int &$offset = 0)
     {
         if (preg_match('/^\s*\<(?P<name>[A-F0-9]+)\>/is', $content, $match)) {
             $name = $match['name'];
diff --git a/src/Smalot/PdfParser/Element/ElementName.php b/src/Smalot/PdfParser/Element/ElementName.php
index 6e8d97ac..0f8d06b9 100644
--- a/src/Smalot/PdfParser/Element/ElementName.php
+++ b/src/Smalot/PdfParser/Element/ElementName.php
@@ -54,7 +54,7 @@ public function equals($value): bool
     /**
      * @return bool|ElementName
      */
-    public static function parse(string $content, ?Document $document = null, int &$offset = 0)
+    public static function parse(string $content, Document $document = null, int &$offset = 0)
     {
         if (preg_match('/^\s*\/([A-Z0-9\-\+,#\.]+)/is', $content, $match)) {
             $name = $match[1];
diff --git a/src/Smalot/PdfParser/Element/ElementNull.php b/src/Smalot/PdfParser/Element/ElementNull.php
index 9af88434..8757630e 100644
--- a/src/Smalot/PdfParser/Element/ElementNull.php
+++ b/src/Smalot/PdfParser/Element/ElementNull.php
@@ -58,7 +58,7 @@ public function equals($value): bool
     /**
      * @return bool|ElementNull
      */
-    public static function parse(string $content, ?Document $document = null, int &$offset = 0)
+    public static function parse(string $content, Document $document = null, int &$offset = 0)
     {
         if (preg_match('/^\s*(null)/s', $content, $match)) {
             $offset += strpos($content, 'null') + \strlen('null');
diff --git a/src/Smalot/PdfParser/Element/ElementNumeric.php b/src/Smalot/PdfParser/Element/ElementNumeric.php
index 5454acc0..80885c17 100644
--- a/src/Smalot/PdfParser/Element/ElementNumeric.php
+++ b/src/Smalot/PdfParser/Element/ElementNumeric.php
@@ -48,7 +48,7 @@ public function __construct(string $value)
     /**
      * @return bool|ElementNumeric
      */
-    public static function parse(string $content, ?Document $document = null, int &$offset = 0)
+    public static function parse(string $content, Document $document = null, int &$offset = 0)
     {
         if (preg_match('/^\s*(?P<value>\-?[0-9\.]+)/s', $content, $match)) {
             $value = $match['value'];
diff --git a/src/Smalot/PdfParser/Element/ElementString.php b/src/Smalot/PdfParser/Element/ElementString.php
index 011bcf46..a18ba5f5 100644
--- a/src/Smalot/PdfParser/Element/ElementString.php
+++ b/src/Smalot/PdfParser/Element/ElementString.php
@@ -54,7 +54,7 @@ public function equals($value): bool
     /**
      * @return bool|ElementString
      */
-    public static function parse(string $content, ?Document $document = null, int &$offset = 0)
+    public static function parse(string $content, Document $document = null, int &$offset = 0)
     {
         if (preg_match('/^\s*\((?P<name>.*)/s', $content, $match)) {
             $name = $match['name'];
diff --git a/src/Smalot/PdfParser/Element/ElementStruct.php b/src/Smalot/PdfParser/Element/ElementStruct.php
index c37b6da4..7c95559c 100644
--- a/src/Smalot/PdfParser/Element/ElementStruct.php
+++ b/src/Smalot/PdfParser/Element/ElementStruct.php
@@ -44,7 +44,7 @@ class ElementStruct extends Element
     /**
      * @return false|Header
      */
-    public static function parse(string $content, ?Document $document = null, int &$offset = 0)
+    public static function parse(string $content, Document $document = null, int &$offset = 0)
     {
         if (preg_match('/^\s*<<(?P<struct>.*)/is', $content)) {
             preg_match_all('/(.*?)(<<|>>)/s', trim($content), $matches);
diff --git a/src/Smalot/PdfParser/Element/ElementXRef.php b/src/Smalot/PdfParser/Element/ElementXRef.php
index ebba71a1..50531a79 100644
--- a/src/Smalot/PdfParser/Element/ElementXRef.php
+++ b/src/Smalot/PdfParser/Element/ElementXRef.php
@@ -83,7 +83,7 @@ public function __toString(): string
     /**
      * @return bool|ElementXRef
      */
-    public static function parse(string $content, ?Document $document = null, int &$offset = 0)
+    public static function parse(string $content, Document $document = null, int &$offset = 0)
     {
         if (preg_match('/^\s*(?P<id>[0-9]+\s+[0-9]+\s+R)/s', $content, $match)) {
             $id = $match['id'];
diff --git a/src/Smalot/PdfParser/Font.php b/src/Smalot/PdfParser/Font.php
index 111a23ba..9e4db9fe 100644
--- a/src/Smalot/PdfParser/Font.php
+++ b/src/Smalot/PdfParser/Font.php
@@ -45,12 +45,12 @@ class Font extends PDFObject
     /**
      * @var array
      */
-    protected $table = null;
+    protected $table;
 
     /**
      * @var array
      */
-    protected $tableSizes = null;
+    protected $tableSizes;
 
     /**
      * Caches results from uchr.
@@ -459,7 +459,7 @@ public function decodeText(array $commands): string
      *
      * @param bool $unicode This parameter is deprecated and might be removed in a future release
      */
-    public function decodeContent(string $text, ?bool &$unicode = null): string
+    public function decodeContent(string $text, bool &$unicode = null): string
     {
         if ($this->has('ToUnicode')) {
             return $this->decodeContentByToUnicodeCMapOrDescendantFonts($text);
diff --git a/src/Smalot/PdfParser/Header.php b/src/Smalot/PdfParser/Header.php
index 66a70102..562897c3 100644
--- a/src/Smalot/PdfParser/Header.php
+++ b/src/Smalot/PdfParser/Header.php
@@ -45,18 +45,18 @@ class Header
     /**
      * @var Document
      */
-    protected $document = null;
+    protected $document;
 
     /**
      * @var Element[]
      */
-    protected $elements = null;
+    protected $elements;
 
     /**
      * @param Element[] $elements list of elements
      * @param Document  $document document
      */
-    public function __construct(array $elements = [], ?Document $document = null)
+    public function __construct(array $elements = [], Document $document = null)
     {
         $this->elements = $elements;
         $this->document = $document;
diff --git a/src/Smalot/PdfParser/PDFObject.php b/src/Smalot/PdfParser/PDFObject.php
index d038702d..c879176b 100644
--- a/src/Smalot/PdfParser/PDFObject.php
+++ b/src/Smalot/PdfParser/PDFObject.php
@@ -56,17 +56,17 @@ class PDFObject
     /**
      * @var Document
      */
-    protected $document = null;
+    protected $document;
 
     /**
      * @var Header
      */
-    protected $header = null;
+    protected $header;
 
     /**
      * @var string
      */
-    protected $content = null;
+    protected $content;
 
     /**
      * @var Config
@@ -75,9 +75,9 @@ class PDFObject
 
     public function __construct(
         Document $document,
-        ?Header $header = null,
-        ?string $content = null,
-        ?Config $config = null
+        Header $header = null,
+        string $content = null,
+        Config $config = null
     ) {
         $this->document = $document;
         $this->header = $header ?? new Header();
@@ -249,7 +249,7 @@ private function getDefaultFont(Page $page = null): Font
     /**
      * @throws \Exception
      */
-    public function getText(?Page $page = null): string
+    public function getText(Page $page = null): string
     {
         $result = '';
         $sections = $this->getSectionsText($this->content);
@@ -283,8 +283,8 @@ public function getText(?Page $page = null): string
                         $args = preg_split('/\s/s', $command[self::COMMAND]);
                         $y = array_pop($args);
                         $x = array_pop($args);
-                        if (((float) $x <= 0) ||
-                            (false !== $current_position_td['y'] && (float) $y < (float) $current_position_td['y'])
+                        if (((float) $x <= 0)
+                            || (false !== $current_position_td['y'] && (float) $y < (float) $current_position_td['y'])
                         ) {
                             // vertical offset
                             $text .= "\n";
@@ -456,7 +456,7 @@ public function getText(?Page $page = null): string
     /**
      * @throws \Exception
      */
-    public function getTextArray(?Page $page = null): array
+    public function getTextArray(Page $page = null): array
     {
         $text = [];
         $sections = $this->getSectionsText($this->content);
@@ -772,7 +772,7 @@ public static function factory(
         Document $document,
         Header $header,
         ?string $content,
-        ?Config $config = null
+        Config $config = null
     ): self {
         switch ($header->get('Type')->getContent()) {
             case 'XObject':
diff --git a/src/Smalot/PdfParser/Page.php b/src/Smalot/PdfParser/Page.php
index 55121a9b..fbc19872 100644
--- a/src/Smalot/PdfParser/Page.php
+++ b/src/Smalot/PdfParser/Page.php
@@ -42,17 +42,17 @@ class Page extends PDFObject
     /**
      * @var Font[]
      */
-    protected $fonts = null;
+    protected $fonts;
 
     /**
      * @var PDFObject[]
      */
-    protected $xobjects = null;
+    protected $xobjects;
 
     /**
      * @var array
      */
-    protected $dataTm = null;
+    protected $dataTm;
 
     /**
      * @return Font[]
@@ -236,9 +236,9 @@ public function getText(self $page = null): string
      */
     public function isFpdf(): bool
     {
-        if (\array_key_exists('Producer', $this->document->getDetails()) &&
-            \is_string($this->document->getDetails()['Producer']) &&
-            0 === strncmp($this->document->getDetails()['Producer'], 'FPDF', 4)) {
+        if (\array_key_exists('Producer', $this->document->getDetails())
+            && \is_string($this->document->getDetails()['Producer'])
+            && 0 === strncmp($this->document->getDetails()['Producer'], 'FPDF', 4)) {
             return true;
         }
 
@@ -926,23 +926,23 @@ public function getTextXY(float $x = null, float $y = null, float $xError = 0, f
             $yTm = (float) $tm[5];
             $text = $item[1];
             if (null === $y) {
-                if (($xTm >= ($x - $xError)) &&
-                    ($xTm <= ($x + $xError))) {
+                if (($xTm >= ($x - $xError))
+                    && ($xTm <= ($x + $xError))) {
                     $extractedData[] = [$tm, $text];
                     continue;
                 }
             }
             if (null === $x) {
-                if (($yTm >= ($y - $yError)) &&
-                    ($yTm <= ($y + $yError))) {
+                if (($yTm >= ($y - $yError))
+                    && ($yTm <= ($y + $yError))) {
                     $extractedData[] = [$tm, $text];
                     continue;
                 }
             }
-            if (($xTm >= ($x - $xError)) &&
-                ($xTm <= ($x + $xError)) &&
-                ($yTm >= ($y - $yError)) &&
-                ($yTm <= ($y + $yError))) {
+            if (($xTm >= ($x - $xError))
+                && ($xTm <= ($x + $xError))
+                && ($yTm >= ($y - $yError))
+                && ($yTm <= ($y + $yError))) {
                 $extractedData[] = [$tm, $text];
                 continue;
             }
diff --git a/src/Smalot/PdfParser/Parser.php b/src/Smalot/PdfParser/Parser.php
index 2109c81f..69ae9b70 100644
--- a/src/Smalot/PdfParser/Parser.php
+++ b/src/Smalot/PdfParser/Parser.php
@@ -60,7 +60,7 @@ class Parser
 
     protected $rawDataParser;
 
-    public function __construct($cfg = [], ?Config $config = null)
+    public function __construct($cfg = [], Config $config = null)
     {
         $this->config = $config ?: new Config();
         $this->rawDataParser = new RawDataParser($cfg, $this->config);
diff --git a/src/Smalot/PdfParser/RawData/RawDataParser.php b/src/Smalot/PdfParser/RawData/RawDataParser.php
index b957a543..1a4583c0 100644
--- a/src/Smalot/PdfParser/RawData/RawDataParser.php
+++ b/src/Smalot/PdfParser/RawData/RawDataParser.php
@@ -402,7 +402,7 @@ protected function decodeXrefStream(string $pdfData, int $startxref, array $xref
                     }
                     $prev_row = $ddata[$k];
                 } // end for each row
-            // complete decoding
+                // complete decoding
             } else {
                 // number of bytes in a row
                 $rowlen = array_sum($wb);
@@ -609,7 +609,7 @@ protected function getObjectVal(string $pdfData, $xref, array $obj): array
      *
      * @return array containing object type, raw value and offset to next object
      */
-    protected function getRawObject(string $pdfData, int $offset = 0, ?array $headerDic = null): array
+    protected function getRawObject(string $pdfData, int $offset = 0, array $headerDic = null): array
     {
         $objtype = ''; // object type to be returned
         $objval = ''; // object value to be returned
diff --git a/tests/PHPUnit/Integration/DocumentTest.php b/tests/PHPUnit/Integration/DocumentTest.php
index 8ab48e30..6a7f8c79 100644
--- a/tests/PHPUnit/Integration/DocumentTest.php
+++ b/tests/PHPUnit/Integration/DocumentTest.php
@@ -50,7 +50,7 @@ protected function getDocumentInstance(): Document
         return new Document();
     }
 
-    protected function getPDFObjectInstance(Document $document, ?Header $header = null): PDFObject
+    protected function getPDFObjectInstance(Document $document, Header $header = null): PDFObject
     {
         return new PDFObject($document, $header);
     }
diff --git a/tests/PHPUnit/TestCase.php b/tests/PHPUnit/TestCase.php
index 08d4739a..5e584c62 100644
--- a/tests/PHPUnit/TestCase.php
+++ b/tests/PHPUnit/TestCase.php
@@ -67,7 +67,7 @@ protected function getElementInstance($value): Element
         return new Element($value);
     }
 
-    protected function getParserInstance(?Config $config = null): Parser
+    protected function getParserInstance(Config $config = null): Parser
     {
         return new Parser([], $config);
     }
diff --git a/tests/Performance/runPerformanceTests.php b/tests/Performance/runPerformanceTests.php
index 7f34b60a..fa983105 100644
--- a/tests/Performance/runPerformanceTests.php
+++ b/tests/Performance/runPerformanceTests.php
@@ -19,6 +19,13 @@
     $time = $endTime - $startTime;
 
     if ($test->getMaxEstimatedTime() <= $time) {
-        throw new PerformanceFailException(sprintf('Performance failed on test "%s". Time taken was %.2f seconds, expected less than %d seconds.', get_class($test), $time, $test->getMaxEstimatedTime()));
+        $msg = sprintf(
+            'Performance failed on test "%s". Time taken was %.2f seconds, expected less than %d seconds.',
+            get_class($test),
+            $time,
+            $test->getMaxEstimatedTime()
+        );
+
+        throw new PerformanceFailException($msg);
     }
 }