public String getProxy() {
    return proxy == null ? null : proxy.toString();
  }
@Test
  public void testInvalidArgumentsForConstructorWithProxy() {
    // Given
    String httpEndpoint = "http://example.com";
    String httpsEndpoint = "https://example.com";
    String proxyURI = null;

    // When/Then
    ConfluentSubmitter submitter = new ConfluentSubmitter(customerId, httpEndpoint,
        httpsEndpoint, proxyURI, null);
    assertTrue(submitter.getProxy() == null);

    proxyURI = "https://proxy.example.com";
    submitter = new ConfluentSubmitter(customerId, httpEndpoint, httpsEndpoint, proxyURI, null);
    assertEquals(proxyURI, submitter.getProxy());
  }