In PermissionMap classe, it write :
void addPermission(final User u, final Permission p) {
List<Permission> permissionList = this.map.get(u.getName());
if (permissionList == null)

{ permissionList = new ArrayList<Permission>(); }

permissionList.add(p);
}

This code cannot work:
if you want to add a new user, the user does not exist in the map, it is impossible to refer to a list of permission would be in the map because it has not been initialized.

The solution is :
void addPermission(final User u, final Permission p) {
List<Permission> permissionList = this.map.get(u.getName());
if (permissionList == null)

{ permissionList = new ArrayList<Permission>(); this.map.put(u.getName(), permissionList); }

permissionList.add(p);
}

Otherwise it would be more correct to write the method "remove" like this:

void removePermission(final User u, final Permission p) {
final List<Permission> permissionList = this.map.get(u.getName());
if (permissionList != null && !permissionList.isEmpty())

{ permissionList.remove(p); }

}