Avoid NPE when callers send null selection args.

Fixes http://b/2226007
diff --git a/core/java/android/content/ContentProviderOperation.java b/core/java/android/content/ContentProviderOperation.java
index 0467516..ca36df2 100644
--- a/core/java/android/content/ContentProviderOperation.java
+++ b/core/java/android/content/ContentProviderOperation.java
@@ -545,8 +545,12 @@
                         "only updates, deletes, and asserts can have selections");
             }
             mSelection = selection;
-            mSelectionArgs = new String[selectionArgs.length];
-            System.arraycopy(selectionArgs, 0, mSelectionArgs, 0, selectionArgs.length);
+            if (selectionArgs == null) {
+                mSelectionArgs = null;
+            } else {
+                mSelectionArgs = new String[selectionArgs.length];
+                System.arraycopy(selectionArgs, 0, mSelectionArgs, 0, selectionArgs.length);
+            }
             return this;
         }