static @NlsContexts.DetailedDescription String checkInterfaceFunctional(@NotNull PsiClass psiClass, @NotNull @Nls String interfaceNonFunctionalMessage) {
    if (psiClass instanceof PsiTypeParameter) return null; //should be logged as cyclic inference
    List<HierarchicalMethodSignature> signatures = LambdaUtil.findFunctionCandidates(psiClass);
    if (signatures == null) return interfaceNonFunctionalMessage;
    if (signatures.isEmpty()) return JavaErrorBundle.message("no.target.method.found");
    if (signatures.size() == 1) {
      return null;
    }
    return JavaErrorBundle.message("multiple.non.overriding.abstract.methods.found.in.interface.0", HighlightUtil.formatClass(psiClass));
  }
static @NlsContexts.DetailedDescription String checkInterfaceFunctional(@NotNull PsiClass psiClass, @NotNull @Nls String interfaceNonFunctionalMessage)