site:effective-site failure with Maven 2

$ mvn org.apache.maven.plugins:maven-site-plugin:3.2:effective-site
[INFO] Scanning for projects...
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[INFO] Building Maven Site Plugin 3
[INFO]    task-segment: [org.apache.maven.plugins:maven-site-plugin:3.2:effective-site]
[INFO] ------------------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] One or more required plugin parameters are invalid/missing for 'site:effective-site'

[0] on the command line, specify: '-Dreports=VALUE'

[INFO] ------------------------------------------------------------------------
[INFO] For more information, run Maven with the -e switch
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2 seconds
[INFO] Finished at: Sun Jan 20 16:13:22 CET 2013
[INFO] Final Memory: 25M/343M
[INFO] ------------------------------------------------------------------------