Fix preg_replace/trim null subject deprecation warnings

Author: abnegate

src/SDK/SDK.php

@@ -741,8 +741,11 @@ protected function render(TemplateWrapper $template, $destination, $block, $para
      * @param string $str
      * @return string
      */
-    protected function helperCamelCase($str)
+    protected function helperCamelCase($str): string
     {
+        if ($str == null) {
+            return '';
+        }
         $str = preg_replace('/[^a-z0-9' . implode("", []) . ']+/i', ' ', $str);
         $str = trim($str);
         $str = ucwords($str);