diff --git a/src/FacebookFactory.php b/src/FacebookFactory.php
index 73324b3f..90f07c4d 100644
--- a/src/FacebookFactory.php
+++ b/src/FacebookFactory.php
@@ -44,7 +44,7 @@ public function buildDriver(array $config)
             ['w3c' => false]
         );
 
-        $capabilities = array_replace($this->guessCapabilities(), $extraCapabilities, $config['capabilities']);
+        $capabilities = array_replace($this->guessCapabilities() ?: [], $extraCapabilities, $config['capabilities']);
 
         // Build driver definition
         return new Definition(FacebookWebDriver::class, [
diff --git a/src/FacebookWebDriver.php b/src/FacebookWebDriver.php
index 1997fa58..aaf4e01e 100755
--- a/src/FacebookWebDriver.php
+++ b/src/FacebookWebDriver.php
@@ -124,7 +124,7 @@ protected function initCapabilities($desiredCapabilities = [])
     {
         // Build base capabilities
         $browserName = $this->getBrowserName();
-        if ($browserName && method_exists(DesiredCapabilities::class, $browserName)) {
+        if ($browserName && method_exists(DesiredCapabilities::class, (string) $browserName)) {
             /** @var DesiredCapabilities $caps */
             $caps = DesiredCapabilities::$browserName();
         } else {
@@ -307,7 +307,7 @@ protected function withSyn()
      */
     protected static function charToOptions($char, $modifier = null)
     {
-        $ord = ord($char);
+        $ord = ord((string) $char);
         if (is_numeric($char)) {
             $ord = $char;
         }
@@ -355,7 +355,7 @@ protected function executeJsOnXpath($xpath, $script, $sync = true)
      */
     private function executeJsOnElement(RemoteWebElement $element, $script, $sync = true)
     {
-        $script  = str_replace('{{ELEMENT}}', 'arguments[0]', $script);
+        $script  = str_replace('{{ELEMENT}}', 'arguments[0]', $script ?: '');
         if ($sync) {
             return $this->webDriver->executeScript($script, [$element]);
         }
@@ -606,7 +606,7 @@ public function getText($xpath)
     {
         $node = $this->findElement($xpath);
         $text = $node->getText();
-        $text = (string) str_replace(array("\r", "\r\n", "\n"), ' ', $text);
+        $text = (string) str_replace(array("\r", "\r\n", "\n"), ' ', $text ?: '');
 
         return $text;
     }
@@ -643,8 +643,8 @@ public function getAttribute($xpath, $name)
     public function getValue($xpath)
     {
         $element = $this->findElement($xpath);
-        $elementName = strtolower($element->getTagName());
-        $elementType = strtolower($element->getAttribute('type'));
+        $elementName = strtolower((string) $element->getTagName());
+        $elementType = strtolower((string) $element->getAttribute('type'));
 
         // Getting the value of a checkbox returns its value if selected.
         if ('input' === $elementName && 'checkbox' === $elementType) {
@@ -712,7 +712,7 @@ public function getValue($xpath)
     public function setValue($xpath, $value)
     {
         $element = $this->findElement($xpath);
-        $elementName = strtolower($element->getTagName());
+        $elementName = strtolower((string) $element->getTagName());
 
         if ('select' === $elementName) {
             if (is_array($value)) {
@@ -731,7 +731,7 @@ public function setValue($xpath, $value)
         }
 
         if ('input' === $elementName) {
-            $elementType = strtolower($element->getAttribute('type'));
+            $elementType = strtolower((string) $element->getAttribute('type'));
 
             if (in_array($elementType, array('submit', 'image', 'button', 'reset'))) {
                 throw new DriverException(sprintf('Impossible to set value an element with XPath "%s" as it is not a select, textarea or textbox', $xpath));
@@ -814,9 +814,9 @@ public function isChecked($xpath)
     public function selectOption($xpath, $value, $multiple = false)
     {
         $element = $this->findElement($xpath);
-        $tagName = strtolower($element->getTagName());
+        $tagName = strtolower((string) $element->getTagName());
 
-        if ('input' === $tagName && 'radio' === strtolower($element->getAttribute('type'))) {
+        if ('input' === $tagName && 'radio' === strtolower((string) $element->getAttribute('type'))) {
             $this->selectRadioValue($element, $value);
 
             return;
@@ -1013,8 +1013,8 @@ public function dragBy($sourceXpath, $xOffset, $yOffset)
      */
     public function executeScript($script)
     {
-        if (preg_match('/^function[\s\(]/', $script)) {
-            $script = preg_replace('/;$/', '', $script);
+        if (preg_match('/^function[\s\(]/', (string) $script)) {
+            $script = preg_replace('/;$/', '', $script ?: '');
             $script = '(' . $script . ')';
         }
 
@@ -1026,7 +1026,7 @@ public function executeScript($script)
      */
     public function evaluateScript($script)
     {
-        if (0 !== strpos(trim($script), 'return ')) {
+        if (0 !== strpos(trim((string) $script), 'return ')) {
             $script = "return {$script};";
         }
 
@@ -1144,7 +1144,7 @@ private function selectRadioValue(RemoteWebElement $element, $value)
 XPATH;
 
                 $xpath = sprintf(
-                    $xpath,
+                    (string) $xpath,
                     $this->xpathEscaper->escapeLiteral($formId),
                     $this->xpathEscaper->escapeLiteral($name),
                     $this->xpathEscaper->escapeLiteral($value)