Fix issue with non-named namespace

php supports a namespace reset using.

```
namespace {
}
```

The odd thing is that a namespace doesn't always have a name like we expected before. To
be able to process this I forced skipping the creation of fqsen. And create it when the real object
is created.

phpDocumentor/phpDocumentor#2967

Author: jaapio

src/phpDocumentor/Reflection/NodeVisitor/ElementNameResolver.php

@@ -87,6 +87,10 @@ public function enterNode(Node $node) : ?int
     {
         switch (get_class($node)) {
             case Namespace_::class:
+                if ($node->name === null) {
+                    break;
+                }
+
                 $this->resetState('\\' . $node->name . '\\');
                 $node->fqsen = new Fqsen($this->buildName());
                 break;

src/phpDocumentor/Reflection/Php/Factory/Namespace_.php

@@ -5,6 +5,7 @@
 namespace phpDocumentor\Reflection\Php\Factory;
 
 use InvalidArgumentException;
+use phpDocumentor\Reflection\Fqsen;
 use phpDocumentor\Reflection\Php\File as FileElement;
 use phpDocumentor\Reflection\Php\ProjectFactoryStrategy;
 use phpDocumentor\Reflection\Php\StrategyContainer;
@@ -40,7 +41,7 @@ public function create(ContextStack $context, object $object, StrategyContainer
 
         $file = $context->peek();
         Assert::isInstanceOf($file, FileElement::class);
-        $file->addNamespace($object->fqsen);
+        $file->addNamespace($object->fqsen ?? new Fqsen('\\'));
         $typeContext = (new NamespaceNodeToContext())($object);
         foreach ($object->stmts as $stmt) {
             $strategy = $strategies->findMatching($context, $stmt);

tests/integration/FileDocblockTest.php

@@ -63,4 +63,22 @@ public function testConditionalFunctionDefine() : void
             $project->getFiles()[$fileName]->getFunctions()
         );
     }
+
+    /**
+     * @covers \phpDocumentor\Reflection\Php\Factory\File::create
+     * @covers \phpDocumentor\Reflection\Php\Factory\File::<private>
+     */
+    public function testGlobalNamespacedFunctionDefine() : void
+    {
+        $fileName =  __DIR__ . '/data/GlobalFiles/global_namspaced_function.php';
+        $project = $this->fixture->create(
+            'MyProject',
+            [new LocalFile($fileName)]
+        );
+
+        $this->assertCount(
+            1,
+            $project->getFiles()[$fileName]->getFunctions()
+        );
+    }
 }

tests/integration/data/GlobalFiles/global_namspaced_function.php

@@ -0,0 +1,23 @@
+<?php
+/**
+ * setup.php - Document the file.
+ *
+ * File long description goes here.
+ *
+ * @author Test Sample
+ */
+
+namespace {
+    /**
+     * autoloader function.
+     *
+     * Function long description goes here.
+     *
+     * @param string $class Namespaced class name
+     * @return void
+     */
+    function libAutoload($class){
+        echo 'Do something';
+    }
+    spl_autoload_register('libAutoload');
+}

tests/unit/phpDocumentor/Reflection/NodeVisitor/ElementNameResolverTest.php

@@ -161,4 +161,18 @@ public function testNamespacedConstant() : void
 
         $this->assertEquals('\\name\\MY_CLASS', (string) $const->fqsen);
     }
+
+    /**
+     * @covers ::enterNode
+     */
+    public function testNoNameNamespace() : void
+    {
+        $const     = new Const_('MY_CLASS', new String_('value'));
+        $namespace = new Namespace_(null);
+
+        $this->fixture->enterNode($namespace);
+        $this->fixture->enterNode($const);
+
+        $this->assertEquals('\\MY_CLASS', (string) $const->fqsen);
+    }
 }