code: public static void checkArgument(boolean expression, @Nullable Object errorMessage) {
      if (!expression) {
        throw new IllegalArgumentException(String.valueOf(errorMessage));
      }
    }
docs: Ensures the truth of an expression involving one or more parameters to the calling method.
  
  @param expression a boolean expression
  @param errorMessage the exception message to use if the check fails; will be converted to a
  string using {@link String#valueOf(Object)}
  @throws IllegalArgumentException if {@code expression} is false