diff --git a/src/Engine.php b/src/Engine.php
index d304078..e5a8889 100644
--- a/src/Engine.php
+++ b/src/Engine.php
@@ -216,6 +216,11 @@ class Engine
 
         $this->article = $this->getArticleByName($this->activeArticle);
 
+        if($this->article === null) {
+            $this->dirty = false;
+            return true;
+        }
+
         // Prefill with defaults
         /** @var Base $option */
         foreach($this->article->getOptions() as $option) {
diff --git a/tests/Customer/G/CalcTest.php b/tests/Customer/G/CalcTest.php
new file mode 100644
index 0000000..dd8f77d
--- /dev/null
+++ b/tests/Customer/G/CalcTest.php
@@ -0,0 +1,42 @@
+<?php
+namespace PSC\Library\Calc\Tests\Customer\G;
+
+use PSC\Library\Calc\Article;
+use PSC\Library\Calc\Engine;
+use PSC\Library\Calc\PaperContainer;
+use PSC\Library\Calc\Tests\Mock\PaperRepostory;
+
+class CalcTest extends \PHPUnit_Framework_TestCase
+{
+
+    /** @var Engine */
+    protected $engine = null;
+
+    public function setUp()
+    {
+        $repository = new PaperRepostory();
+
+        $paperContainer = new PaperContainer();
+        $paperContainer->parse(simplexml_load_string(file_get_contents(__DIR__ . '/papierContainer.xml')));
+
+        $this->engine = new Engine();
+        $this->engine->setPaperContainer($paperContainer);
+        $this->engine->setPaperRepository($repository);
+        $this->engine->setFormulas(file_get_contents(__DIR__ . '/formels.txt'));
+        $this->engine->setParameters(file_get_contents(__DIR__ . '/parameters.txt'));
+        $this->engine->setTemplates(file_get_contents(__DIR__ . '/calcTemplates.xml'));
+
+        $this->engine->loadString(file_get_contents(__DIR__ . '/calc.xml'));
+
+    }
+
+    public function tearDown()
+    {
+        $this->engine = null;
+    }
+
+    public function testIfDefaultPriceIsOk()
+    {
+        $this->assertEquals(10.49 , $this->engine->getPrice());
+    }
+}
\ No newline at end of file
diff --git a/tests/Customer/G/calc.xml b/tests/Customer/G/calc.xml
new file mode 100644
index 0000000..3e06b62
--- /dev/null
+++ b/tests/Customer/G/calc.xml
@@ -0,0 +1,60 @@
+<?xml version="1.0" encoding="utf-8"?>
+<kalkulation>
+    <artikel>
+        <name>Zubehör</name>
+        <kommentar></kommentar>
+
+        <option id="auflage" name="Menge" type="Input" step="100" default="100" min="100" max="10000" help="Geben Sie die gewünschte Menge in 100 Stückschritten ein"/>
+
+
+        <option id="variante" name="Kettenlänge" type="Select" default="10">
+            <opt id="10" name="50 mm"></opt>
+            <opt id="20" name="100 mm"></opt>
+            <opt id="30" name="150 mm"></opt>
+            <opt id="40" name="200 mm"></opt>
+            <opt id="50" name="250 mm"></opt>
+            <opt id="60" name="300 mm"></opt>
+        </option>
+
+        <!-- Einzelpreisermittlung -->
+        <option id="preisstaffel" name="preisstaffel" type="Hidden" default="10">
+            <variante>
+                <grenze formel="(0.41*(pow($Vauflage$V,-0.296))*$Vauflage$V)">10</grenze>
+                <grenze formel="(0.36*(pow($Vauflage$V,-0.264))*$Vauflage$V)">20</grenze>
+                <grenze formel="(0.46*(pow($Vauflage$V,-0.246))*$Vauflage$V)">30</grenze>
+                <grenze formel="(0.51*(pow($Vauflage$V,-0.229))*$Vauflage$V)">40</grenze>
+                <grenze formel="(0.59*(pow($Vauflage$V,-0.226))*$Vauflage$V)">50</grenze>
+                <grenze formel="(0.63*(pow($Vauflage$V,-0.218))*$Vauflage$V)">60</grenze>
+            </variante>
+        </option>
+
+
+        <!-- Preisberechung Basis Sprintis Online Staffel-->
+        <option id="kosten_kugelkette" name="kosten_kugelkette" type="Hidden" default="1">
+            <auflage>
+                <grenze formel="($CVpreisstaffel$CV*($Pzuschlag_zubehoer_extern$P))">1-</grenze>
+            </auflage>
+        </option>
+
+        <!-- Lieferzeit Gesamt DISPLAY  -->
+        <option id="lieferzeit_gesamt_display" name="lieferzeit_gesamt_display" type="Hidden" default="1" displayOnly="1">
+            <auflage>
+                <grenze formel="5">-1</grenze>
+            </auflage>
+        </option>
+
+
+        <!-- Gesamtgewicht  -->
+        <option id="weight" name="weight" type="Hidden" default="1">
+            <variante>
+                <grenze formel="($Vauflage$V*2)">10</grenze>
+                <grenze formel="($Vauflage$V*3)">20</grenze>
+                <grenze formel="($Vauflage$V*4)">30</grenze>
+                <grenze formel="($Vauflage$V*5)">40</grenze>
+                <grenze formel="($Vauflage$V*6)">50</grenze>
+                <grenze formel="($Vauflage$V*7)">60</grenze>
+            </variante>
+        </option>
+
+    </artikel>
+</kalkulation>
\ No newline at end of file
diff --git a/tests/Customer/G/calcTemplates.xml b/tests/Customer/G/calcTemplates.xml
new file mode 100644
index 0000000..b3f7d62
--- /dev/null
+++ b/tests/Customer/G/calcTemplates.xml
@@ -0,0 +1,4 @@
+<root>
+
+
+</root>
diff --git a/tests/Customer/G/formels.txt b/tests/Customer/G/formels.txt
new file mode 100644
index 0000000..e69de29
diff --git a/tests/Customer/G/papierContainer.xml b/tests/Customer/G/papierContainer.xml
new file mode 100644
index 0000000..8ec6de3
--- /dev/null
+++ b/tests/Customer/G/papierContainer.xml
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<container>
+
+</container>
\ No newline at end of file
diff --git a/tests/Customer/G/parameters.txt b/tests/Customer/G/parameters.txt
new file mode 100644
index 0000000..e69de29