docs: @Restricted(DoNotUse.class)
      public AutoCompletionCandidates doAutoCompleteCopyNewItemFrom(@QueryParameter final String value, @AncestorInPath ItemGroup<?> container) {
          AutoCompletionCandidates candidates = AutoCompletionCandidates.ofJobNames(TopLevelItem.class, value, container);
          if (container instanceof DirectlyModifiableTopLevelItemGroup) {
              DirectlyModifiableTopLevelItemGroup modifiableContainer = (DirectlyModifiableTopLevelItemGroup) container;
              Iterator<String> it = candidates.getValues().iterator();
              while (it.hasNext()) {
                  TopLevelItem item = Jenkins.getInstance().getItem(it.next(), container, TopLevelItem.class);
                  if (item == null) {
                      continue; // ?
                  }
                  if (!modifiableContainer.canAdd(item)) {
                      it.remove();
                  }
              }
          }
          return candidates;
      }