public Optional<String> getCredentialsFile()
    {
        return credentialsFile;
    }
@Test
    public void testExplicitPropertyMappingsWithCredentialsFile()
    {
        Map<String, String> properties = new ImmutableMap.Builder<String, String>()
                .put("bigquery.credentials-file", "cfile")
                .build();

        ConfigurationFactory configurationFactory = new ConfigurationFactory(properties);
        BigQueryConfig config = configurationFactory.build(BigQueryConfig.class);

        assertEquals(config.getCredentialsFile(), Optional.of("cfile"));
    }