public void setOutputFormat(OutputFormat outputFormat) {
        if (outputFormat == null) {
            throw new IllegalArgumentException("outputFormat can not be null");
        }
        this.outputFormat = outputFormat;
    }
Set the output format for the validation

@param outputFormat
           {@link OutputFormat}, not {@code null}
@throws IllegalArgumentException
            if argument is {@code null}
src/nu/validator/client/EmbeddedValidator.java