Filter by category should also be tested for undefined (and not just empty string) in case no category has been defined.
src.dir = src
lib.dir = lib
doc.dir = doc
build.dir = build
product.name = yuicompressor
version.number = 2.4.2
jar.name = ${product.name}-${version.number}.jar
dist.package.name = ${product.name}-${version.number}