Add a test for setDataSource(null)

This is a test for "Fix NullpointerException in MediaMetadataRetriever"
with id 425916e in MediaMetadataRetriever

Change-Id: Iff0bda5e035893824525b9f4ec9c023cef13c898
diff --git a/tests/tests/media/src/android/media/cts/MediaMetadataRetrieverTest.java b/tests/tests/media/src/android/media/cts/MediaMetadataRetrieverTest.java
index b090e27..da54171 100644
--- a/tests/tests/media/src/android/media/cts/MediaMetadataRetrieverTest.java
+++ b/tests/tests/media/src/android/media/cts/MediaMetadataRetrieverTest.java
@@ -70,4 +70,15 @@
         assertNull("Writer was unexpected present",
                 retriever.extractMetadata(MediaMetadataRetriever.METADATA_KEY_WRITER));
     }
+
+    public void testSetDataSourceNull() {
+        MediaMetadataRetriever retriever = new MediaMetadataRetriever();
+
+        try {
+            retriever.setDataSource((String)null);
+            fail("Expected IllegalArgumentException.");
+        } catch (IllegalArgumentException ex) {
+            // Expected, test passed.
+        }
+    }
 }