More fixes

src/models/User.java

@@ -11,15 +11,12 @@ public class User implements Model {
     private String email;
     private String name;
     private String role;
-    private List<Certificate> certificates;
+    private List<Certificate> certificates = new ArrayList<>();
 
     /* This constructor is necessary for JSON parsing */
     public User() {}
 
     public void addCertificate(Certificate certificate) {
-        if (this.certificates == null) {
-            this.certificates = new ArrayList<>();
-        }
         this.certificates.add(certificate);
     }
 

src/resources/users.json

@@ -30,14 +30,14 @@
   "password" : "8c6976e5b5410415bde908bd4dee15dfb167a9c873fc4bb8a81f6f2ab448a918",
   "role" : "Admin"
 }, {
-  "certificates" : null,
+  "certificates" : [ ],
   "email" : "ahmed@gmail.com",
   "id" : 4,
   "name" : "ahmed sherif",
   "password" : "8d969eef6ecad3c29a3a629280e686cf0c3f5d5a86aff3ca12020c923adc6c92",
   "role" : "Instructor"
 }, {
-  "certificates" : null,
+  "certificates" : [ ],
   "email" : "malek@gmail.com",
   "id" : 5,
   "name" : "malek",