TT#65101 expand now fills the same key only once

* the same key is now expanded only once to use the same
  data ref otherwise expand like
  contract_id.contact_id,contract_id.billing_profile_id
  makes it so that 2nd contract_id would overwrite the already
  existing (expanded) contract_id

Change-Id: I6cab67c2f549e9165dbf2cfd2f4b84daef503dd8

lib/NGCP/Panel/Role/API.pm

@@ -1370,7 +1370,7 @@ sub expand_field {
             }
         }
     } else {
-        $resource->{$to} =
+        $resource->{$to} ||=
             $self->get_expanded_field_data($c, $expand, $resource, $field, $class, $form, $id);
         if ($subfield) {
             $found = $self->expand_field($c, $resource->{$to}, $form, $subfield);