Added null tests.

spring-ldap/src/test/java/org/springframework/ldap/core/DirContextAdapterTest.java

@@ -27,7 +27,6 @@ import javax.naming.directory.ModificationItem;
 
 import junit.framework.TestCase;
 
-
 /**
  * Tests the DirContextAdapter class.
  * 
@@ -681,6 +680,18 @@ public class DirContextAdapterTest extends TestCase {
         assertEquals("nisse hult", modificationAttribute.get());
     }
 
+    public void testGetStringAttributes_NullValue() {
+        String result = classUnderTest
+                .getStringAttribute("someAbsentAttribute");
+        assertNull(result);
+    }
+
+    public void testGetStringAttributes_AttributeExists_NullValue() {
+        classUnderTest.setAttribute(new BasicAttribute("someAttribute", null));
+        String result = classUnderTest.getStringAttribute("someAttribute");
+        assertNull(result);
+    }
+
     private ModificationItem getModificationItem(ModificationItem[] mods,
             int operation) {
         for (int i = 0; i < mods.length; i++) {