@Contract("null->false")
  private static boolean checkProvider(@Nullable DocumentationProvider provider) {
    if (provider == null) return false;
    if (provider instanceof CompositeDocumentationProvider
        && ContainerUtil.or(((CompositeDocumentationProvider)provider).getAllProviders(), p -> p instanceof HtmlDocumentationProvider)) {
      Logger.getInstance(HtmlDocumentationProvider.class)
        .error(
          "An 'HtmlDocumentationProvider' is most likely registered through 'com.intellij.documentationProvider' extension point instead of 'com.intellij.lang.documentationProvider'. Recurrent behaviour has been prevented.");
      return false;
    }
    return true;
  }
@Contract("null->false")
  private static boolean checkProvider(@Nullable DocumentationProvider provider)