code: static Throwable checkedException(final Throwable ex) {
          Validate.isTrue(ex != null && !(ex instanceof RuntimeException)
                  && !(ex instanceof Error), "Not a checked exception: " + ex);
  
          return ex;
      }
docs: Tests whether the specified {@code Throwable} is a checked exception. If
  not, an exception is thrown.
  
  @param ex the {@code Throwable} to check
  @return a flag whether the passed in exception is a checked exception
  @throws IllegalArgumentException if the {@code Throwable} is not a
  checked exception