Overload newSpannerBatchUpdateException to avoid breakages

Author: odeke-em

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerExceptionFactory.java

@@ -139,6 +139,11 @@ public static SpannerException newSpannerException(Throwable cause, XGoogSpanner
     return newSpannerException(null, cause, reqId);
   }
 
+  public static SpannerBatchUpdateException newSpannerBatchUpdateException(
+      ErrorCode code, String message, long[] updateCounts) {
+    return newSpannerBatchUpdateException(code, message, updateCounts, null);
+  }
+
   public static SpannerBatchUpdateException newSpannerBatchUpdateException(
       ErrorCode code, String message, long[] updateCounts, @Nullable XGoogSpannerRequestId reqId) {
     DoNotConstructDirectly token = DoNotConstructDirectly.ALLOWED;