Fix issue that caused IniWriter to fail on empty configs

library/Icinga/File/Ini/Dom/Document.php

@@ -67,6 +67,7 @@ class Document
      */
     public function render()
     {
+        $sections = array();
         foreach ($this->sections as $section) {
             $sections []=  $section->render();
         }

library/Icinga/File/Ini/Dom/Section.php

@@ -7,7 +7,7 @@ class Section
 {
     /**
      * @var string
-     *
+     */
     protected $name;
 
     /**

library/Icinga/File/Ini/IniWriter.php

@@ -178,8 +178,9 @@ class IniWriter
                 Logger::warning('Section-less property ' . (string)$directives . ' was ignored.');
                 continue;
             }
-            $newSection = $newconfig->getSection($section);
-            if (isset($newSection)) {
+
+            if ($newconfig->hasSection($section)) {
+                $newSection = $newconfig->getSection($section);
                 $oldDomSection = $doc->getSection($section);
                 foreach ($directives as $key => $value) {
                     if ($value instanceof ConfigObject) {