The class under models package implements serializable interface to support native image(GraalVM).

Author: nilchina

src/main/java/org/gitlab4j/api/models/ProjectFetches.java

@@ -36,8 +36,8 @@ public void setDate(Date date) {
         }
     }
 
-    public static class Fetches {
-
+    public static class Fetches implements Serializable {
+        private static final long serialVersionUID = 4630780820005787008L;
         private Integer total;
         private List<DateCount> days;