Handle falsy header elements, fixes #514 (#525)

Author: dsuurlant

src/Smalot/PdfParser/Header.php

@@ -132,8 +132,8 @@ public function has(string $name): bool
      */
     public function get(string $name)
     {
-        if (\array_key_exists($name, $this->elements)) {
-            return $this->resolveXRef($name);
+        if (\array_key_exists($name, $this->elements) && $element = $this->resolveXRef($name)) {
+            return $element;
         }
 
         return new ElementMissing();

src/Smalot/PdfParser/PDFObject.php

@@ -78,7 +78,7 @@ public function __construct(
         ?Config $config = null
     ) {
         $this->document = $document;
-        $this->header = null !== $header ? $header : new Header();
+        $this->header = $header ?? new Header();
         $this->content = $content;
         $this->config = $config;
     }

tests/Integration/HeaderTest.php

@@ -155,6 +155,18 @@ public function testGet(): void
         $this->assertTrue($header->get('Font') instanceof Page);
         $this->assertTrue($header->get('Image') instanceof ElementMissing);
         $this->assertTrue($header->get('Resources') instanceof ElementMissing);
+
+        /**
+         * A double forward slash in the header's content results in a falsy element
+         * that should be parsed to ElementMissing instead.
+         *
+         * @see https://github.com/smalot/pdfparser/pull/525
+         */
+        $content = '<</Type/Page/SubType//Text>>foo';
+        $position = 0;
+        $header = Header::parse($content, $document, $position);
+
+        $this->assertTrue($header->get('SubType') instanceof ElementMissing);
     }
 
     public function testResolveXRef(): void