将第9章从zk essentials导入Eclipse Kepler EE，因为Maven Project可以工作，但是在导入第10章时：
安装JPA 2.0时失败。
java.lang.NullPointerException
at org.eclipse.jpt.common.core.internal.resource.ModuleResourceLocator.getRootFolder(ModuleResourceLocator.java:85)
at org.eclipse.jpt.common.core.internal.resource.ModuleResourceLocator.getDefaultLocation(ModuleResourceLocator.java:32)
at org.eclipse.jpt.common.core.internal.resource.SimpleProjectResourceLocator.getDefaultLocation(SimpleProjectResourceLocator.java:45)
at org.eclipse.jpt.jpa.core.internal.facet.JpaFacetInstallDelegate.defaultResourceLocation(JpaFacetInstallDelegate.java:123)
at org.eclipse.jpt.jpa.core.internal.facet.JpaFacetInstallDelegate.createPersistenceXml(JpaFacetInstallDelegate.java:107)
at org.eclipse.jpt.jpa.core.internal.facet.JpaFacetInstallDelegate.createProjectXml(JpaFacetInstallDelegate.java:100)
at org.eclipse.jpt.jpa.core.internal.facet.JpaFacetInstallDelegate.execute_(JpaFacetInstallDelegate.java:61)
at org.eclipse.jpt.jpa.core.internal.facet.JpaFacetActionDelegate.execute(JpaFacetActionDelegate.java:35)
at org.eclipse.wst.common.project.facet.core.internal.FacetedProject.callDelegate(FacetedProject.java:1477)
at org.eclipse.wst.common.project.facet.core.internal.FacetedProject.modifyInternal(FacetedProject.java:441)
at org.eclipse.wst.common.project.facet.core.internal.FacetedProject.mergeChangesInternal(FacetedProject.java:1181)
at org.eclipse.wst.common.project.facet.core.internal.FacetedProject.access$2(FacetedProject.java:1117)
at org.eclipse.wst.common.project.facet.core.internal.FacetedProject$5.run(FacetedProject.java:1099)
at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:2345)
at org.eclipse.wst.common.project.facet.core.internal.FacetedProject.mergeChanges(FacetedProject.java:1109)
at org.eclipse.wst.common.project.facet.core.internal.FacetedProjectWorkingCopy.commitChanges(FacetedProjectWorkingCopy.java:2020)
at org.eclipse.wst.common.project.facet.ui.ModifyFacetedProjectWizard.performFinish(ModifyFacetedProjectWizard.java:400)
at org.eclipse.wst.common.project.facet.ui.ModifyFacetedProjectWizard$3.run(ModifyFacetedProjectWizard.java:331)
at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:2345)
at org.eclipse.wst.common.project.facet.ui.ModifyFacetedProjectWizard$4.run(ModifyFacetedProjectWizard.java:345)
at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:121)
感谢任何指导，帮助！
答案 0 :(得分：4)
我通过查看this comment on JBIDE-11655解决了这个问题：删除了我的项目文件夹中的所有.project，.settings和.classpath。