code: public OverridingBodyFileOption overrideBodyFile(String subject, String plainBody) {
          assertArgumentNotNull("subject", subject);
          assertArgumentNotNull("plainBody", plainBody);
          if (bodyFile == null) {
              throw new IllegalStateException("No body file so mistake?: specified-subject=" + subject);
          }
          clearBodyFile();
          setSubject(subject);
          final DirectBodyOption option = useDirectBody(plainBody);
          return new OverridingBodyFileOption(option);
      }
docs: -----------------