Actually if you have five keys or less you can just use .of() instead of the builder: http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/collect/ImmutableMap.html#of(K, V) 

so in this case:

        ImmutableMap.of(
            "QUIET", WarningLevel.QUIET,
            "DEFAULT", WarningLevel.DEFAULT,
            "VERBOSE", WarningLevel.VERBOSE);