added testmethod indexTestFour in TextTest.java

test/TextTest.java

@@ -109,4 +109,13 @@ public class TextTest {
         stringListe = txt.index();
         Assertions.assertEquals(0, stringListe.size());
     }
+
+    /**
+     * Test Method to check if index is working with empty Strings
+     */
+    @Test
+    void indexTestFour() {
+        txt.add("");
+        txt.index();
+    }
 }