String requiredMavenVersion = (String) result.getProperties().get("prerequisites.maven");
            if (requiredMavenVersion != null) {
                Map<String, String> props = new LinkedHashMap<>(pluginArtifact.getProperties());
                props.put("requiredMavenVersion", requiredMavenVersion);
                pluginArtifact = pluginArtifact.setProperties(props);
            }

        String checkValue = "value";

        Properties properties = new Properties();
        properties.setProperty(key, checkValue);

        Model model = new Model();
        model.setProperties(properties);

        MavenProject project = new MavenProject(model);

        ExpressionEvaluator ee = createExpressionEvaluator(project, null, new Properties());

                // a parameter.

                value = properties.getProperty(expression);
            }

            if ((value == null) && ((project != null) && (project.getProperties() != null))) {
                value = project.getProperties().getProperty(expression);
            }
        }

        if (value instanceof String) {
            // TODO without #, this could just be an evaluate call...

    }

    protected List<ValueSource> createValueSources(
            Model model, Path projectDir, ModelBuilderRequest request, ModelProblemCollector problems) {
        Map<String, String> modelProperties = model.getProperties();

        ValueSource projectPrefixValueSource;
        ValueSource prefixlessObjectBasedValueSource;
        if (request.getValidationLevel() >= ModelBuilderRequest.VALIDATION_LEVEL_MAVEN_4_0) {

    Map<String, String> getUserProperties();

    /**
     * Returns immutable system properties to use for interpolation. The system properties are collected from the
     * runtime environment such as {@link System#getProperties()} and environment variables
     * (prefixed with {@code env.}).
     *
     * @return the system properties, never {@code null}
     */
    @Nonnull
    Map<String, String> getSystemProperties();

    /**

    }

    /**
     * Gets the system properties to use for interpolation and profile activation. The system properties are collected
     * from the runtime environment like {@link System#getProperties()} and environment variables.
     *
     * @return The system properties, never {@code null}.
     */
    public Properties getSystemProperties() {
        return request.getSystemProperties();
    }

        String key = "m2.name";
        String checkValue = "value";

        MavenProject project = createDefaultProject();
        project.getModel().getProperties().setProperty(key, checkValue);

        ExpressionEvaluator ee = createExpressionEvaluator(project, new Properties());

        Object value = ee.evaluate("${" + key + "}");

            }

            activation.packaging(modelActivation.getPackaging());

            profile.activation(activation.build());
        }

        profile.properties(modelProfile.getProperties().entrySet().stream()
                .collect(Collectors.toMap(
                        e -> e.getKey().toString(), e -> e.getValue().toString())));

            HashMap<String, String> result = new HashMap<>(getSystemProperties());
            if (project != null) {
                result.putAll(project.getModel().getProperties());
            }
            result.putAll(getUserProperties());
            return result;
        }

        @Override
        public Version getMavenVersion() {
            return null;

            final Model model, final File projectDir, final ProjectBuilderConfiguration config) {
        String timestampFormat = DEFAULT_BUILD_TIMESTAMP_FORMAT;

        Properties modelProperties = model.getProperties();
        if (modelProperties != null) {
            timestampFormat = modelProperties.getProperty(BUILD_TIMESTAMP_FORMAT_PROPERTY, timestampFormat);
        }