Use correct check before using expungeMessageUri

Bug: 6918040
Change-Id: I75b6791e273a7a7f091db96d5b226f2607e94aef
diff --git a/src/com/android/mail/compose/ComposeActivity.java b/src/com/android/mail/compose/ComposeActivity.java
index 3cca1d8..866ab24 100644
--- a/src/com/android/mail/compose/ComposeActivity.java
+++ b/src/com/android/mail/compose/ComposeActivity.java
@@ -2519,7 +2519,7 @@
             if (mDraftId != UIProvider.INVALID_MESSAGE_ID) {
                 ContentValues values = new ContentValues();
                 values.put(BaseColumns._ID, mDraftId);
-                if (mAccount.expungeMessageUri != null) {
+                if (!mAccount.expungeMessageUri.equals(Uri.EMPTY)) {
                     getContentResolver().update(mAccount.expungeMessageUri, values, null, null);
                 } else {
                     getContentResolver().delete(mDraft.uri, null, null);