Issue #345 Fix type mismatch error for cat command

Author: mikehaertl

src/Pdf.php

@@ -181,8 +181,12 @@ public function cat(
         ?string $rotation = null,
     ): self {
         $this->getCommand()
-            ->setOperation('cat')
-            ->addPageRange($start, $end, $handle, $qualifier, $rotation);
+            ->setOperation('cat');
+
+        if ($start !== null) {
+            $this->getCommand()
+                ->addPageRange($start, $end, $handle, $qualifier, $rotation);
+        }
         return $this;
     }