I'm not actually getting a NPE, but I am able to reproduce the problem reported in bug 4401373. I'm using jdk 1.4.0_02 on Solaris with ant 1.4.1. I was told to file a new bug if it was reproducible in 1.4. Here's my output:
    [javac] <mypath>/MyJavaFile.java:286: cannot access org.openide.util.Task
    [javac] file org/openide/util/Task.class not found
    [javac] public ActionLoaderFolder (final DataFolder folder)
    [javac] ^
    [javac] Note: Some input files use or override a deprecated API.
    [javac] Note: Recompile with -deprecation for details.
    [javac] 1 error