add getFirstHeader method to ElasticsearchResponse

client/src/main/java/org/elasticsearch/client/ElasticsearchResponse.java

@@ -77,6 +77,19 @@ public class ElasticsearchResponse implements Closeable {
         return response.getAllHeaders();
     }
 
+    /**
+     * Returns the value of the first header with a specified name of this message.
+     * If there is more than one matching header in the message the first element is returned.
+     * If there is no matching header in the message <code>null</code> is returned.
+     */
+    public String getFirstHeader(String name) {
+        Header header = response.getFirstHeader(name);
+        if (header == null) {
+            return null;
+        }
+        return header.getValue();
+    }
+
     /**
      * Returns the response body available, null otherwise
      * @see HttpEntity