Merge pull request #12497 from oyiadom/master

Update BulkProcessor.java

core/src/main/java/org/elasticsearch/action/bulk/BulkProcessor.java

@@ -145,6 +145,10 @@ public class BulkProcessor implements Closeable {
     }
 
     public static Builder builder(Client client, Listener listener) {
+        if (client == null) {
+            throw new NullPointerException("The client you specified while building a BulkProcessor is null");
+        }
+        
         return new Builder(client, listener);
     }