Polishing.

(cherry picked from commit d3e8c9f)

Author: sothawo

src/main/java/org/springframework/data/elasticsearch/client/util/RequestConverters.java

@@ -1452,7 +1452,8 @@ private static String encodePart(String pathPart) {
 				// encode each part (e.g. index, type and id) separately before merging them into the path
 				// we prepend "/" to the path part to make this path absolute, otherwise there can be issues with
 				// paths that start with `-` or contain `:`
-				URI uri = new URI((String)null, "", "/" + pathPart, (String)null, (String)null);
+				// the authority must be an empty string and not null, else paths that being with slashes could have them
+				URI uri = new URI((String) null, "", "/" + pathPart, (String) null, (String) null);
 				// manually encode any slash that each part may contain
 				return uri.getRawPath().substring(1).replaceAll("/", "%2F");
 			} catch (URISyntaxException e) {