Mojo accessing project properties

[David Jackman]

I'm trying to write a mojo that accesses the properties section of the
project pom.  I declared a member variable like this
    /**
     * Project properties.
     *
     * @parameter default-value="${project.properties}"
     * @required
     * @readonly
     */
    private Properties properties;
When my mojo runs, it gets a Properties object okay, but it's always
empty, even if I have declared properties in the project POM.
 
Am I doing something wrong?  How do I access the project properties (not
plugin configuration properties)?
 
..David..