}

    private MavenProject getProject(Artifact artifact) {
        return getAllProjects()
                .getOrDefault(artifact.getGroupId(), Collections.emptyMap())
                .getOrDefault(artifact.getArtifactId(), Collections.emptyMap())
                .getOrDefault(artifact.getBaseVersion(), null);
    }

    // groupId -> (artifactId -> (version -> project)))

        }
        sessionBuilder.setAuthenticationSelector(authSelector);

        Object transport = mergedProps.getOrDefault(MAVEN_RESOLVER_TRANSPORT_KEY, MAVEN_RESOLVER_TRANSPORT_DEFAULT);
        if (MAVEN_RESOLVER_TRANSPORT_DEFAULT.equals(transport)) {
            // The "default" mode (user did not set anything) from now on defaults to AUTO

     *
     * - a `getFooOrDefault(@CheckForNull Foo defaultValue)` method that returns
     *   `map.getOrDefault(FOO_KEY, defaultValue)`
     *
     * - a call that consults a chain of maps, as in `mapA.getOrDefault(key, mapB.getOrDefault(key,
     *   ...))`
     *
     * So it makes sense for the parameter (and thus the return type) to be @CheckForNull.
     *
     * Two other points:
     *