### Question:
X509BundleSet implements BundleSource<X509Bundle> { public static X509BundleSet emptySet() { return new X509BundleSet(); } private  X509BundleSet(final Map<TrustDomain, X509Bundle> bundles); private  X509BundleSet(); static X509BundleSet of(@NonNull final Collection<X509Bundle> bundles); static X509BundleSet emptySet(); void put(@NonNull final X509Bundle x509Bundle); @Override X509Bundle getBundleForTrustDomain(@NonNull final TrustDomain trustDomain); Map<TrustDomain, X509Bundle> getBundles();  }### Answer:
@Test void testEmptySet() { X509BundleSet x509BundleSet = X509BundleSet.emptySet(); assertNotNull(x509BundleSet); assertEquals(0, x509BundleSet.getBundles().size()); }