Replace .equals("") with .isEmpty()

Use the more idiomatic String.isEmpty() method instead of comparing
against an empty string literal. This expresses the intent more
clearly and is the standard Java convention for empty string checks.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: oschwald

src/main/java/com/maxmind/geoip2/WebServiceClient.java

@@ -413,7 +413,7 @@ private void handle4xxStatus(HttpResponse<InputStream> response)
         var uri = response.uri();
 
         final var body = readBody(response);
-        if (body.equals("")) {
+        if (body.isEmpty()) {
             throw new HttpException("Received a " + status + " error for "
                 + uri + " with no body", status, uri);
         }