Need a way to reference a config property from another property using the expression language in a mojo

Example:

/**

• @parameter
• @required
  */
  private String cloverOutputDirectory;

/**

• @parameter expression="$ {cloverOutputDirectory}/clover.db"
  * @required
  */
  private String cloverDatabase;
  
  
  I'd like that the cloverDatabase variable gets set to ${cloverOutputDirectory}

  /clover.db

ATM the value is null/clover.db even though cloverOutputDirectory get sets to a non-null value