public void removePackageRepository(String id) {
        PackageRepository packageRepositoryToBeDeleted = this.find(id);
        if (packageRepositoryToBeDeleted == null) {
            throw new RuntimeException(String.format("Could not find repository with id '%s'", id));
        }
        this.remove(packageRepositoryToBeDeleted);
    }
@Test
    void shouldReturnNullExceptionWhenRepoIdIsNotFound() throws Exception {
        PackageRepositories packageRepositories = new PackageRepositories();
        try {
            packageRepositories.removePackageRepository("repo1");
            fail("This should have thrown an exception");
        } catch (Exception e) {
            assertThat(e.getMessage()).isEqualTo(String.format("Could not find repository with id '%s'", "repo1"));
        }
    }