java.lang.NullPointerException
   at java.util.TreeMap.put(TreeMap.java:563)
   at java.util.TreeSet.add(TreeSet.java:255)
   at java.util.AbstractCollection.addAll(AbstractCollection.java:344)
   at java.util.TreeSet.addAll(TreeSet.java:312)
   at org.netbeans.orm.converter.compiler.ClassDefSnippet.getImportSnippets(ClassDefSnippet.java:379)
   at sun.reflect.NativeMethodAccessorImpl.invoke0(NativeMethodAccessorImpl.java:0)
   at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.lang.reflect.Method.invoke(Method.java:497)
   at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.doInvoke(UberspectImpl.java:389)
   at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:378)
Caused: org.apache.velocity.exception.MethodInvocationException: Invocation of method 'getImportSnippets' in  class org.netbeans.orm.converter.generator.managed.ManagedClassDefSnippet threw exception java.lang.NullPointerException at jpatemplate.vm[line 8, column 42]
   at org.apache.velocity.runtime.parser.node.ASTMethod.handleInvocationException(ASTMethod.java:337)
   at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:284)
   at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:252)
   at org.apache.velocity.runtime.parser.node.ASTReference.value(ASTReference.java:487)
   at org.apache.velocity.runtime.directive.Foreach.render(Foreach.java:280)
   at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:175)
   at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:336)
   at org.apache.velocity.Template.merge(Template.java:328)
   at org.apache.velocity.Template.merge(Template.java:235)
Caused: org.netbeans.orm.converter.compiler.InvalidDataException: Class name : fr.ensimag.livret.entity.User
   at org.netbeans.orm.converter.compiler.ClassDefSnippet.getSnippet(ClassDefSnippet.java:337)
   at org.netbeans.orm.converter.util.ORMConverterUtil.writeSnippet(ORMConverterUtil.java:247)
   at org.netbeans.orm.converter.generator.managed.ManagedClassModuleGeneratorImpl.generateEntityClasses(ManagedClassModuleGeneratorImpl.java:104)
   at org.netbeans.orm.converter.generator.managed.ManagedClassModuleGeneratorImpl.generate(ManagedClassModuleGeneratorImpl.java:67)
   at org.netbeans.jpa.modeler.source.generator.adaptor.internal.JPASourceCodeGenerator.generate(JPASourceCodeGenerator.java:42)
   at org.netbeans.jpa.modeler.source.generator.task.SourceCodeGeneratorTask.exportCode(SourceCodeGeneratorTask.java:86)
   at org.netbeans.jpa.modeler.source.generator.task.SourceCodeGeneratorTask.begin(SourceCodeGeneratorTask.java:70)
   at org.netbeans.modeler.task.AbstractNBTask.beginTask(AbstractNBTask.java:462)
   at org.netbeans.modeler.task.AbstractNBTask.run(AbstractNBTask.java:114)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1423)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2033)