diff --git a/src/XMLSecEnc.php b/src/XMLSecEnc.php
index 39a1f3cb..36101928 100644
--- a/src/XMLSecEnc.php
+++ b/src/XMLSecEnc.php
@@ -70,16 +70,16 @@ class XMLSecEnc
     /** @var string */
     public const XMLENCNS = 'http://www.w3.org/2001/04/xmlenc#';
 
-    /** @var null|\DOMDocument */
+    /** @var \DOMDocument|null */
     private $encdoc = null;
 
-    /** @var null|\DOMNode  */
+    /** @var \DOMNode|null */
     private $rawNode = null;
 
-    /** @var null|string */
+    /** @var string|null */
     public $type = null;
 
-    /** @var null|\DOMElement */
+    /** @var \DOMElement|null */
     public $encKey = null;
 
     /** @var array */
@@ -111,10 +111,6 @@ private function resetTemplate(): void
      */
     public function addReference(string $name, DOMNode $node, string $type): void
     {
-        if (!($node instanceof DOMNode)) {
-            throw new Exception('$node is not of type DOMNode');
-        }
-
         $curencdoc = $this->encdoc;
         $this->resetTemplate();
         $encdoc = $this->encdoc;
@@ -143,24 +139,28 @@ public function setNode(DOMNode $node): void
      * @param bool $replace Whether the encrypted node should be replaced in the original tree. Default is true.
      * @throws \Exception
      *
-     * @return \DOMElement  The <xenc:EncryptedData>-element.
+     * @return \DOMNode|false  The <xenc:EncryptedData>-element.
      */
-    public function encryptNode(XMLSecurityKey $objKey, bool $replace = true): DOMElement
+    public function encryptNode(XMLSecurityKey $objKey, bool $replace = true)
     {
         $data = '';
         if (empty($this->rawNode)) {
             throw new Exception('Node to encrypt has not been set');
         }
+
         if (!($objKey instanceof XMLSecurityKey)) {
             throw new Exception('Invalid Key');
         }
+
         $doc = $this->rawNode->ownerDocument;
         $xPath = new DOMXPath($this->encdoc);
         $objList = $xPath->query('/xenc:EncryptedData/xenc:CipherData/xenc:CipherValue');
+
         $cipherValue = $objList->item(0);
         if ($cipherValue == null) {
             throw new Exception('Error locating CipherValue element within template');
         }
+
         switch ($this->type) {
             case (self::ELEMENT):
                 $data = $doc->saveXML($this->rawNode);
@@ -556,7 +556,7 @@ public static function staticLocateKeyInfo(XMLSecurityKey $objBaseKey = null, DO
      * @param \DOMNode|null $node
      * @return \RobRichards\XMLSecLibs\XMLSecurityKey|null
      */
-    public function locateKeyInfo(XMLSecurityKey $objBaseKey = null, DOMNode $node = null): XMLSecurityKey
+    public function locateKeyInfo(XMLSecurityKey $objBaseKey = null, DOMNode $node = null): ?XMLSecurityKey
     {
         if (empty($node)) {
             $node = $this->rawNode;
diff --git a/src/XMLSecurityDSig.php b/src/XMLSecurityDSig.php
index 81f81284..4de3d431 100644
--- a/src/XMLSecurityDSig.php
+++ b/src/XMLSecurityDSig.php
@@ -305,7 +305,6 @@ private function canonicalizeData(
 
         if (
             is_null($arXPath)
-            && ($node instanceof DOMNode)
             && ($node->ownerDocument !== null)
             && $node->isSameNode($node->ownerDocument->documentElement)
         ) {
@@ -432,9 +431,9 @@ public function validateDigest(DOMNode $refNode, string $data): bool
      * @param \DOMNode $refNode
      * @param \DOMNode $objData
      * @param bool $includeCommentNodes
-     * @return string
+     * @return \DOMNode|string
      */
-    public function processTransforms(DOMNode $refNode, DOMNode $objData, bool $includeCommentNodes = true): string
+    public function processTransforms(DOMNode $refNode, DOMNode $objData, bool $includeCommentNodes = true)
     {
         $data = $objData;
         $xpath = new DOMXPath($refNode->ownerDocument);
@@ -822,7 +821,7 @@ public function addReferenceList(
 
 
     /**
-     * @param \DOMElement|string $data
+     * @param \DOMElement $data
      * @param string|null $mimetype
      * @param string|null $encoding
      * @return \DOMElement
diff --git a/src/XMLSecurityKey.php b/src/XMLSecurityKey.php
index 12db2d99..2ad9ca8b 100644
--- a/src/XMLSecurityKey.php
+++ b/src/XMLSecurityKey.php
@@ -842,9 +842,9 @@ public function serializeKey($parent): void
      * Will return the X509 certificate in PEM-format if this key represents
      * an X509 certificate.
      *
-     * @return string The X509 certificate or null if this key doesn't represent an X509-certificate.
+     * @return string|null The X509 certificate or null if this key doesn't represent an X509-certificate.
      */
-    public function getX509Certificate(): string
+    public function getX509Certificate(): ?string
     {
         return $this->x509Certificate;
     }
@@ -857,9 +857,9 @@ public function getX509Certificate(): string
      *  The thumbprint as a lowercase 40-character hexadecimal number, or null
      *  if this isn't a X509 certificate.
      *
-     *  @return string Lowercase 40-character hexadecimal number of thumbprint
+     *  @return string|null Lowercase 40-character hexadecimal number of thumbprint
      */
-    public function getX509Thumbprint(): string
+    public function getX509Thumbprint(): ?string
     {
         return $this->X509Thumbprint;
     }