Deal with the case when there are no existing client role mappings for

the user(ie, it's a first time for an update).

@@ -227,8 +227,8 @@ void updateUser(RealmResource realm, String keycloakClientId, String keycloakUse
 
     List<RoleRepresentation> toRemove = []
     RoleMappingResource roleMappingResource = userResource.roles()
-    ClientMappingsRepresentation clientMappingsRespresentation = roleMappingResource.getAll().getClientMappings()[keycloakClientId]
-    for (RoleRepresentation existingRoleRep: clientMappingsRespresentation.getMappings()) {
+    ClientMappingsRepresentation clientMappingsRespresentation = roleMappingResource.getAll().getClientMappings()?[keycloakClientId]
+    for (RoleRepresentation existingRoleRep: clientMappingsRespresentation?.getMappings()) {
         if (!wantedClientRoles.remove(existingRoleRep.getName())) {
             toRemove.add(existingRoleRep)
         }