"ant jar" build failure

[skywalkerlw]

I got following "ant jar" build failure:
BUILD FAILED
/Users/bournewang/Downloads/android-viewflow-master 3/viewflow/build.xml:10: /Users/bournewang/Downloads/android-viewflow-master 3/viewflow/bin does not exist.

Total time: 0 seconds
BournetekiMacBook-Pro-2:viewflow bournewang$ ant jar
Buildfile: /Users/bournewang/Downloads/android-viewflow-master 3/viewflow/build.xml

Then i add a directory with name of bin, and build again:

jar:
[jar] Building MANIFEST-only jar: /Users/bournewang/Downloads/android-viewflow-master 3/viewflow/android-viewflow.jar

BUILD SUCCESSFUL
Total time: 0 seconds

However, the size of generated android-viewflow.jar is only 350bytes and obviously, it's not correct.