public class DeleteDocumentAction extends ActionSupport {

   private static final long serialVersionUID = 2640141927469006062L;
   private String project_id; //currently has no use//wanted to re-populate setup-project.jsp
   private String document_id;
   
   public String execute(){
      Session s = HibernateUtil.getSessionFactory().openSession();
//      s.createQuery("delete from Document d where d.id="+document_id).executeUpdate();
//      s.close();
//      s = HibernateUtil.getSessionFactory().openSession();
      List<String> content_id = (List<String>)s.createQuery("c.id from Content c where c.document="+document_id).list();//<<ERROR
//      s.createQuery("delete from Content c where c.document="+document_id).executeUpdate();
      
//      String c_id;
//      for(int i=0;!content_id.isEmpty();){
//         c_id = (String)content_id.get(i);
//         System.out.println("DeleteDocument>Got Content id>"+c_id);
//         s.createQuery("delete from Translation t where t.expression="+c_id);
//         
//      }
      
      s.close();
      return SUCCESS;
   }

@Entity
@Table (name = "DOC_CONTENT")
public class Content {
   private Long id;
   private Document document;
   private int position;
   private String expression;
   private List<Translation> translations;
   private int translationLanguage;
   
   public void setDocument(Document doc) {
      this.document = doc;
   }
   
   @ManyToOne(cascade=CascadeType.ALL)
   @JoinColumn(name="document_fk")
   public Document getDocument() {
      return document;
   }
   
   public void setExpression(String expression) {
      this.expression = expression;
   }

   @Column(name = "expression")
   public String getExpression() {
      return expression;
   }
   
   public void setTranslations(List<Translation> translation) {
      this.translations = translation;
   }
   
   @OneToMany(targetEntity=net.translators.logic.documents.Translation.class,
         cascade=CascadeType.ALL,mappedBy="expression", fetch=FetchType.EAGER)
   public List<Translation> getTranslations() {
      if(translations == null)
         translations = new ArrayList<Translation>();
      return this.translations;
   }
   
   public void addTranslation(Translation translation){
      getTranslations().add(translation);
   }
   public void setTranslationLanguage(int translationLanguage) {
      this.translationLanguage = translationLanguage;
   }
   
   @Column(name = "translation_language")
   public int getTranslationLanguage() {
      return translationLanguage;
   }

   public void setId(Long id) {
      this.id = id;
   }

   @Id
   @GeneratedValue
   public Long getId() {
      return id;
   }

   public void setPosition(int position) {
      this.position = position;
   }

   @GeneratedValue(strategy=GenerationType.SEQUENCE)
   @Column(name="position")
   public int getPosition() {
      return position;
   }
   
}

@Entity
@Table(name="DOCUMENTS")
public class Document {
   private String name;
   private int[] translateTo;
   private int writtenLang;
   private Project project;
   private List<Content> content;
   private Long id;
   
   public void removeTranslationLang(int lang){
      
   }
   public void setDocLang(int lang){
      
   }
   public void setId(Long id) {
      this.id = id;
   }
   
   @Id @GeneratedValue
   @Column(name="id")
   public Long getId() {
      return id;
   }
   public void setName(String name) {
      this.name = name;
   }
   
   @Column(name="name")
   public String getName() {
      return name;
   }
   
   public void setProject(Project project) {
      this.project = project;
   }
   
   @ManyToOne(cascade=CascadeType.ALL)
   @JoinColumn(name="project_fk")
   public Project getProject() {
      return project;
   }
   
   public String toString(){
      return getName();
   }
   public void setContent(List<Content> content) {
      this.content = content;
   }
   
   @OneToMany (mappedBy="document", cascade=CascadeType.ALL, orphanRemoval=true)
   public List<Content> getContent() {
      return content;
   }
}

   <action name="do-delete-document" class="net.translators.actions.document.DeleteDocumentAction">
      <interceptor-ref name="defaultAndloginVerifier"/>
      <result name="success" type="redirect">home</result>
      <result name="input">/organization/setup-project.jsp</result>
      <result name="error">/organization/setup-project.jsp</result>
      <result name="login" type="redirect">login-user</result>
   </action>

Hibernate:
    /*
from
    Document d
where
    d.project=1 */ select
        document0_.id as id2_,
        document0_.name as name2_,
        document0_.project_fk as project3_2_
    from
        DOCUMENTS document0_
    where
        document0_.project_fk=1

Struts has detected an unhandled exception:
Messages:    
node to traverse cannot be null!
File:    org/hibernate/hql/ast/util/NodeTraverser.java
Line number:    63
Stacktraces
java.lang.IllegalArgumentException: node to traverse cannot be null!

    org.hibernate.hql.ast.util.NodeTraverser.traverseDepthFirst(NodeTraverser.java:63)
    org.hibernate.hql.ast.QueryTranslatorImpl.parse(QueryTranslatorImpl.java:280)
    org.hibernate.hql.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:182)
    org.hibernate.hql.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:136)
    org.hibernate.engine.query.HQLQueryPlan.(HQLQueryPlan.java:101)
    org.hibernate.engine.query.HQLQueryPlan.(HQLQueryPlan.java:80)
    org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:124)
    org.hibernate.impl.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:156)
    org.hibernate.impl.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:135)
    org.hibernate.impl.SessionImpl.createQuery(SessionImpl.java:1770)
    net.translators.actions.document.DeleteDocumentAction.execute(DeleteDocumentAction.java:23)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    java.lang.reflect.Method.invoke(Method.java:597)
    com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:452)
    com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:291)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:254)
    net.translators.interceptors.MyValidator.intercept(MyValidator.java:74)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:176)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:263)
    org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:133)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:190)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:243)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:142)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:166)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:176)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:190)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:187)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
    org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:485)
    org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
    org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)
    org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:244)
    org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
    org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:161)
    org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:541)
    org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:383)
    org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:243)
    org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
    org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:288)
    java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    java.lang.Thread.run(Thread.java:662)