### Question:
MavenRepository implements ClassLoaderFactory { public boolean exists( MavenId mavenId ) throws MavenRepositoryException { if (mavenId == null) return false; Set<MavenId> existing = exists(mavenId, (MavenId)null); return existing.contains(mavenId); } MavenRepository( final MavenUrlProvider urlProvider ); ClassLoader getClassLoader( ClassLoader parent,
                                       MavenId... mavenIds ); ClassLoader getClassLoader( String... coordinates ); ClassLoader getClassLoader( ClassLoader parent,
                                       String... coordinates ); boolean exists( MavenId mavenId ); Set<MavenId> exists( MavenId firstId,
                                MavenId... mavenIds ); List<MavenDependency> getDependencies( MavenId mavenId ); URL getUrl( MavenId mavenId,
                       ArtifactType artifactType,
                       SignatureType signatureType ); URL getUrl( MavenId mavenId,
                       ArtifactType artifactType,
                       SignatureType signatureType,
                       boolean createIfRequired );  }### Answer:
@Test public void shouldConsiderNullIdToNotExist() { assertThat(maven.exists((MavenId)null), is(false)); }
@Test public void shouldReturnEmptySetWhenPassedAllNullIdsForCheckingWhetherProjectsExist() { assertThat(maven.exists(null, (MavenId)null), is(notNullValue())); assertThat(maven.exists(null, (MavenId)null).size(), is(0)); assertThat(maven.exists(null, (MavenId)null), is(notNullValue())); assertThat(maven.exists(null, (MavenId)null).size(), is(0)); }