return Collections.unmodifiableList(build.getExtensions());
        }
    }

    public void addProjectReference(MavenProject project) {
        projectReferences.put(
                getProjectReferenceId(project.getGroupId(), project.getArtifactId(), project.getVersion()), project);
    }

    public Properties getProperties() {
        return getModel().getProperties();
    }