Problem compiling plugins

[Pau <pa...@gmail.com>]

Hello,
I have to implement a plugin for Nutch 0.9, so I have followed the
WritingPluginExample-0.9.
When I try to compile the plugins I get warnings about
nutch-extensionpoints.jar:
      [jar] Warning: skipping jar archive
/home/pau/Pau/Master/Tesis/nutch-0.9/build/nutch-extensionpoints/nutch-extensionpoints.jar
because no files were in
Why do I get this warning?

Furthermore, when I try to compile the .war file with the command 'ant war',
I get the following error:
generate-locale:
     [echo] Generating docs for locale=ca
     [xslt] java.lang.ClassNotFoundException:
org.apache.tools.ant.taskdefs.optional.TraXLiaison
     [xslt]     at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
     [xslt]     at java.security.AccessController.doPrivileged(Native
Method)
     [xslt]     at
java.net.URLClassLoader.findClass(URLClassLoader.java:188)
     [xslt]     at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
     [xslt]     at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
     [xslt]     at
java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
     [xslt]     at java.lang.Class.forName0(Native Method)
     [xslt]     at java.lang.Class.forName(Class.java:169)
     [xslt]     at
org.apache.tools.ant.taskdefs.XSLTProcess.loadClass(XSLTProcess.java:548)
     [xslt]     at
org.apache.tools.ant.taskdefs.XSLTProcess.resolveProcessor(XSLTProcess.java:533)
     [xslt]     at
org.apache.tools.ant.taskdefs.XSLTProcess.getLiaison(XSLTProcess.java:785)
     [xslt]     at
org.apache.tools.ant.taskdefs.XSLTProcess.execute(XSLTProcess.java:300)
     [xslt]     at
org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:288)
     [xslt]     at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown
Source)
     [xslt]     at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
     [xslt]     at java.lang.reflect.Method.invoke(Method.java:597)
     [xslt]     at
org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:105)
     [xslt]     at org.apache.tools.ant.Task.perform(Task.java:348)
     [xslt]     at org.apache.tools.ant.Target.execute(Target.java:357)
     [xslt]     at org.apache.tools.ant.Target.performTasks(Target.java:385)
     [xslt]     at
org.apache.tools.ant.Project.executeSortedTargets(Project.java:1329)
     [xslt]     at
org.apache.tools.ant.helper.SingleCheckExecutor.executeTargets(SingleCheckExecutor.java:38)
     [xslt]     at
org.apache.tools.ant.Project.executeTargets(Project.java:1181)
     [xslt]     at org.apache.tools.ant.taskdefs.Ant.execute(Ant.java:416)
     [xslt]     at
org.apache.tools.ant.taskdefs.CallTarget.execute(CallTarget.java:105)
     [xslt]     at
org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:288)
     [xslt]     at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown
Source)
     [xslt]     at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
     [xslt]     at java.lang.reflect.Method.invoke(Method.java:597)
     [xslt]     at
org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:105)
     [xslt]     at org.apache.tools.ant.Task.perform(Task.java:348)
     [xslt]     at org.apache.tools.ant.Target.execute(Target.java:357)
     [xslt]     at org.apache.tools.ant.Target.performTasks(Target.java:385)
     [xslt]     at
org.apache.tools.ant.Project.executeSortedTargets(Project.java:1329)
     [xslt]     at
org.apache.tools.ant.Project.executeTarget(Project.java:1298)
     [xslt]     at
org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExecutor.java:41)
     [xslt]     at
org.apache.tools.ant.Project.executeTargets(Project.java:1181)
     [xslt]     at org.apache.tools.ant.Main.runBuild(Main.java:698)
     [xslt]     at org.apache.tools.ant.Main.startAnt(Main.java:199)
     [xslt]     at
org.apache.tools.ant.launch.Launcher.run(Launcher.java:257)
     [xslt]     at
org.apache.tools.ant.launch.Launcher.main(Launcher.java:104)

BUILD FAILED
/home/pau/Pau/Master/Tesis/nutch-0.9/build.xml:442: The following error
occurred while executing this line:
/home/pau/Pau/Master/Tesis/nutch-0.9/build.xml:408:
java.lang.ClassNotFoundException:
org.apache.tools.ant.taskdefs.optional.TraXLiaison

Could you please help me with it?
Thank you very much.