*
     * @param model The model to create a source hint for, may be {@code null}.
     * @return The user-friendly source hint, never {@code null}.
     */
    static String toSourceHint(Model model) {
        if (model == null) {
            return "";
        }

        StringBuilder buffer = new StringBuilder(128);

        buffer.append(toId(model));

                problems.add(new ModelProblemCollectorRequest(Severity.ERROR, ModelProblem.Version.BASE)
                        .setMessage("Invalid packaging for parent POM " + ModelProblemUtils.toSourceHint(parentModel)
                                + ", must be \"pom\" but is \"" + parentModel.getPackaging() + "\"")
                        .setLocation(parentModel.getLocation("packaging")));
            }
        }