@NotNull
  public SdkReferenceItem addSdkReferenceItem(@NotNull SdkType type,
                                              @NotNull String name,
                                              @Nullable String versionString,
                                              boolean isValid) {
    SdkReferenceItem element = new SdkReferenceItem(type, name, versionString, isValid);
    //similar element might already be included!
    removeSdkReferenceItem(element);

    ImmutableList.Builder<SdkReferenceItem> builder = ImmutableList.builder();
    builder.addAll(myReferenceItems);
    builder.add(element);

    myReferenceItems = builder.build();
    syncModel();

    return element;
  }
@NotNull
  public SdkReferenceItem addSdkReferenceItem(@NotNull SdkType type,
                                              @NotNull String name,
                                              @Nullable String versionString,
                                              boolean isValid)