Attempt at deleting threads

So far no rules are activated and it just puts the infrastructure in place.
Rules can be added in separately after discussion among the developers,
along with fixing any violations of the rules.

Co-authored-by: Nico Athanassiadis <nico@dsv.su.se>
Reviewed-on: #138
Reviewed-by: Nico Athanassiadis <nico@dsv.su.se>
Co-authored-by: Andreas Svanberg <andreass@dsv.su.se>
Co-committed-by: Andreas Svanberg <andreass@dsv.su.se>

Dockerfile

@@ -24,6 +24,7 @@ COPY test-data/src/ test-data/src/
 RUN ./mvnw package \
     --define skipTests \
     --activate-profiles branch,DEV \
+    --define checkstyle.skip=true \
     --define skip.npm \
     --define skip.installnodenpm
 

checkstyle.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0"?>
+<!DOCTYPE module PUBLIC
+        "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
+        "https://checkstyle.org/dtds/configuration_1_3.dtd">
+
+<module name="Checker">
+</module>

core/pom.xml

@@ -32,6 +32,10 @@
             <groupId>org.glassfish.jersey.media</groupId>
             <artifactId>jersey-media-json-jackson</artifactId>
         </dependency>
+        <dependency>
+            <groupId>org.glassfish.jersey.inject</groupId>
+            <artifactId>jersey-hk2</artifactId>
+        </dependency>
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-context</artifactId>

core/src/main/java/se/su/dsv/scipro/forum/BasicForumService.java

@@ -32,5 +32,10 @@ public interface BasicForumService extends Serializable {
 
     boolean canDelete(ForumPost forumPost);
 
-    void deletePost(ForumPost post);
+    Deletion deletePost(ForumPost post);
+
+    enum Deletion {
+        SINGLE_POST,
+        ENTIRE_THREAD,
+    }
 }

core/src/main/java/se/su/dsv/scipro/forum/BasicForumServiceImpl.java

@@ -185,15 +185,17 @@ public class BasicForumServiceImpl implements BasicForumService {
 
     @Override
     @Transactional
-    public void deletePost(ForumPost post) {
+    public Deletion deletePost(ForumPost post) {
         if (!canDelete(post)) {
             throw new PostCantBeDeletedException();
         }
         if (isInitialPost(post)) {
             threadRepository.delete(post.getForumThread());
+            return Deletion.ENTIRE_THREAD;
         } else {
             post.setDeleted(true);
             postRepository.save(post);
+            return Deletion.SINGLE_POST;
         }
     }
 

core/src/main/java/se/su/dsv/scipro/forum/ProjectForumService.java

@@ -24,4 +24,8 @@ public interface ProjectForumService {
     List<Pair<ProjectThread, ForumPost>> latestPost(Project a, int amount);
 
     long getUnreadThreadsCount(Project project, User user);
+
+    boolean canDelete(ProjectThread projectThread, ForumPost forumPost);
+
+    void deletePost(ProjectThread projectThread, ForumPost forumPost);
 }

core/src/main/java/se/su/dsv/scipro/forum/ProjectForumServiceImpl.java

@@ -121,6 +121,20 @@ public class ProjectForumServiceImpl implements ProjectForumService {
         return basicForumService.countUnreadThreads(list, user);
     }
 
+    @Override
+    public boolean canDelete(ProjectThread projectThread, ForumPost forumPost) {
+        return basicForumService.canDelete(forumPost);
+    }
+
+    @Override
+    @Transactional
+    public void deletePost(ProjectThread projectThread, ForumPost forumPost) {
+        BasicForumService.Deletion deletion = basicForumService.deletePost(forumPost);
+        if (deletion == BasicForumService.Deletion.ENTIRE_THREAD) {
+            projectThreadRepository.delete(projectThread);
+        }
+    }
+
     @Override
     public ProjectThread findOne(long threadId) {
         return projectThreadRepository.findOne(threadId);

core/src/main/java/se/su/dsv/scipro/match/IdeaServiceImpl.java

@@ -235,10 +235,8 @@ public class IdeaServiceImpl extends AbstractServiceImpl<Idea, Long> implements
             if (authorParticipatingOnActiveIdea(coAuthor, ap)) {
                 return new Pair<>(Boolean.FALSE, PARTNER_ALREADY_PARTICIPATING_ERROR);
             }
-            if (
-                coAuthor.getDegreeType() != ProjectType.UNKNOWN &&
-                coAuthor.getDegreeType() != idea.getProjectType().getDegreeType()
-            ) {
+            List<ProjectType> typesForCoAuthor = applicationPeriodService.getTypesForStudent(ap, coAuthor);
+            if (!typesForCoAuthor.contains(idea.getProjectType())) {
                 return new Pair<>(Boolean.FALSE, WRONG_LEVEL_FOR_YOUR_PARTNER);
             }
             if (!projectService.getActiveProjectsByUserAndProjectType(coAuthor, idea.getProjectType()).isEmpty()) {

core/src/main/xsd/daisy_api.xsd

@@ -559,7 +559,7 @@
 
     <xs:complexType name="course">
         <xs:sequence>
-            <xs:element name="courseCode" type="xs:string" minOccurs="0">
+            <xs:element name="courseCode" type="xs:string" minOccurs="1">
             </xs:element>
             <xs:element name="credits" type="xs:float" minOccurs="1">
             </xs:element>
@@ -567,6 +567,8 @@
             </xs:element>
             <xs:element name="level" type="educationalLevel" minOccurs="0">
             </xs:element>
+            <xs:element name="degreeThesisCourse" type="xs:boolean" minOccurs="1">
+            </xs:element>
             <xs:element name="eduInstDesignation" type="xs:string" minOccurs="1">
             </xs:element>
         </xs:sequence>

core/src/test/java/se/su/dsv/scipro/forum/BasicForumServiceIntegrationTest.java

@@ -5,6 +5,7 @@ import static org.hamcrest.Matchers.contains;
 import static org.hamcrest.Matchers.hasItem;
 import static org.hamcrest.Matchers.not;
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
@@ -57,7 +58,10 @@ public class BasicForumServiceIntegrationTest extends IntegrationTest {
         setLoggedInAs(commenter);
 
         assertTrue(basicForumService.canDelete(reply));
-        assertDoesNotThrow(() -> basicForumService.deletePost(reply));
+        assertDoesNotThrow(() -> {
+            BasicForumService.Deletion deletion = basicForumService.deletePost(reply);
+            assertEquals(BasicForumService.Deletion.SINGLE_POST, deletion);
+        });
     }
 
     @Test
@@ -204,7 +208,8 @@ public class BasicForumServiceIntegrationTest extends IntegrationTest {
 
         setLoggedInAs(op);
 
-        basicForumService.deletePost(post);
+        BasicForumService.Deletion deletion = basicForumService.deletePost(post);
+        assertEquals(BasicForumService.Deletion.ENTIRE_THREAD, deletion);
 
         ForumThread threadById = basicForumService.findThreadById(thread.getId());
         assertNull(threadById, "Thread was not deleted");

core/src/test/java/se/su/dsv/scipro/match/IdeaServiceImplTest.java

@@ -241,6 +241,7 @@ public class IdeaServiceImplTest {
         when(generalSystemSettingsService.getGeneralSystemSettingsInstance()).thenReturn(new GeneralSystemSettings());
         Idea idea = createBachelorIdea(Idea.Status.UNMATCHED);
         when(applicationPeriodService.getTypesForStudent(applicationPeriod, student)).thenReturn(List.of(bachelor));
+        when(applicationPeriodService.getTypesForStudent(applicationPeriod, coAuthor)).thenReturn(List.of(bachelor));
 
         Pair<Boolean, String> acceptance = ideaService.validateStudentAcceptance(
             idea,
@@ -401,6 +402,39 @@ public class IdeaServiceImplTest {
         assertEquals(expected, ideaService.countAuthorsByApplicationPeriod(applicationPeriod, params));
     }
 
+    @Test
+    public void wrong_type_for_author() {
+        when(applicationPeriodService.getTypesForStudent(applicationPeriod, student)).thenReturn(List.of(master));
+        when(applicationPeriodService.getTypesForStudent(applicationPeriod, coAuthor)).thenReturn(List.of(bachelor));
+
+        assertPair(
+            false,
+            "The idea is the wrong level for you, please pick another one.",
+            ideaService.validateStudentAcceptance(
+                createBachelorIdea(Idea.Status.UNMATCHED),
+                student,
+                coAuthor,
+                applicationPeriod
+            )
+        );
+    }
+
+    @Test
+    public void wrong_type_for_partner() {
+        when(applicationPeriodService.getTypesForStudent(applicationPeriod, coAuthor)).thenReturn(List.of(master));
+
+        assertPair(
+            false,
+            "The idea is the wrong level for your partner, please pick another one.",
+            ideaService.validateStudentAcceptance(
+                createBachelorIdea(Idea.Status.UNMATCHED),
+                student,
+                coAuthor,
+                applicationPeriod
+            )
+        );
+    }
+
     private Idea mockInactiveIdea() {
         Idea idea = new Idea();
         Match match = new Match();

core/src/test/java/se/su/dsv/scipro/report/GradingReportServiceImplIntegrationTest.java

@@ -6,7 +6,11 @@ import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.google.common.eventbus.EventBus;
+import com.sun.net.httpserver.HttpServer;
 import jakarta.inject.Inject;
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.nio.charset.StandardCharsets;
 import java.time.LocalDate;
 import java.time.Month;
 import java.util.*;
@@ -15,6 +19,9 @@ import org.junit.jupiter.api.Test;
 import se.su.dsv.scipro.finalseminar.FinalSeminar;
 import se.su.dsv.scipro.finalseminar.FinalSeminarOpposition;
 import se.su.dsv.scipro.finalseminar.OppositionApprovedEvent;
+import se.su.dsv.scipro.grading.GetGradeError;
+import se.su.dsv.scipro.grading.GradingServiceImpl;
+import se.su.dsv.scipro.grading.Result;
 import se.su.dsv.scipro.project.Project;
 import se.su.dsv.scipro.security.auth.roles.Roles;
 import se.su.dsv.scipro.system.DegreeType;
@@ -149,6 +156,44 @@ public class GradingReportServiceImplIntegrationTest extends IntegrationTest {
         assertNull(oppositionCriterion.getFeedback());
     }
 
+    @Test
+    public void test_json_deserialization() throws IOException {
+        String json =
+            """
+            {
+                "grade": "A",
+                "reported": "2021-01-01"
+            }
+            """;
+        HttpServer httpServer = startHttpServerWithJsonResponse(json);
+
+        int port = httpServer.getAddress().getPort();
+
+        GradingServiceImpl gradingService = new GradingServiceImpl("http://localhost:" + port);
+        Either<GetGradeError, Optional<Result>> result = gradingService.getResult("token", 1, 2, 3);
+
+        Optional<Result> right = result.right();
+        assertTrue(right.isPresent());
+        assertEquals(LocalDate.of(2021, 1, 1), right.get().reported());
+
+        httpServer.stop(0);
+    }
+
+    private static HttpServer startHttpServerWithJsonResponse(String json) throws IOException {
+        HttpServer httpServer = HttpServer.create();
+        httpServer.createContext("/", exchange -> {
+            try (exchange) {
+                byte[] response = json.getBytes(StandardCharsets.UTF_8);
+                exchange.getResponseHeaders().add("Content-Type", "application/json");
+                exchange.sendResponseHeaders(200, response.length);
+                exchange.getResponseBody().write(response);
+            }
+        });
+        httpServer.bind(new InetSocketAddress("localhost", 0), 0);
+        httpServer.start();
+        return httpServer;
+    }
+
     private void addOppositionCriterion() {
         gradingReportTemplate = createOppositionCriteria(gradingReportTemplate, 2);
         gradingReport = createGradingReport(project, student);

pom.xml

@@ -26,7 +26,7 @@
         <wicket.version>10.4.0</wicket.version>
         <jakarta.persistence-api.version>3.1.0</jakarta.persistence-api.version>
         <querydsl.version>5.0.0</querydsl.version>
-        <poi.version>5.2.5</poi.version>
+        <poi.version>5.4.0</poi.version>
 
         <!--
             When updating spring-boot check if the transitive dependency on json-smart has been
@@ -211,6 +211,11 @@
                     <artifactId>maven-war-plugin</artifactId>
                     <version>3.4.0</version>
                 </plugin>
+                <plugin>
+                    <groupId>org.apache.maven.plugins</groupId>
+                    <artifactId>maven-checkstyle-plugin</artifactId>
+                    <version>3.6.0</version>
+                </plugin>
             </plugins>
         </pluginManagement>
         <plugins>
@@ -312,6 +317,23 @@
                     </execution>
                 </executions>
             </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-checkstyle-plugin</artifactId>
+                <configuration>
+                    <configLocation>checkstyle.xml</configLocation>
+                    <failOnViolation>true</failOnViolation>
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>validate</id>
+                        <phase>process-sources</phase>
+                        <goals>
+                            <goal>check</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
         </plugins>
     </build>
 </project>

test-data/src/main/java/se/su/dsv/scipro/testdata/BaseData.java

@@ -1,6 +1,9 @@
 package se.su.dsv.scipro.testdata;
 
+import java.util.List;
+import se.su.dsv.scipro.match.Keyword;
 import se.su.dsv.scipro.system.ProjectType;
+import se.su.dsv.scipro.system.ResearchArea;
 
 /// All the base test data that can be re-used in different test cases.
 ///
@@ -16,4 +19,11 @@ public interface BaseData {
     ProjectType bachelor();
     ProjectType magister();
     ProjectType master();
+
+    /**
+     * @return generic research area with some keywords attached to it
+     */
+    ResearchAreaAndKeywords researchArea();
+
+    record ResearchAreaAndKeywords(ResearchArea researchArea, List<Keyword> keywords) {}
 }

test-data/src/main/java/se/su/dsv/scipro/testdata/DataInitializer.java

@@ -2193,6 +2193,11 @@ public class DataInitializer implements Lifecycle, BaseData, Factory {
         return createEmployee(firstName);
     }
 
+    @Override
+    public ResearchAreaAndKeywords researchArea() {
+        return new ResearchAreaAndKeywords(researchArea1, List.of(keyword1, keyword2));
+    }
+
     private static final class SimpleTextFile implements FileUpload {
 
         private final User uploader;

test-data/src/main/java/se/su/dsv/scipro/testdata/populators/PartnerTypeExemption.java

@@ -0,0 +1,68 @@
+package se.su.dsv.scipro.testdata.populators;
+
+import jakarta.inject.Inject;
+import java.time.LocalDate;
+import java.time.LocalDateTime;
+import java.util.Set;
+import org.springframework.stereotype.Service;
+import se.su.dsv.scipro.match.ApplicationPeriod;
+import se.su.dsv.scipro.match.ApplicationPeriodService;
+import se.su.dsv.scipro.match.Idea;
+import se.su.dsv.scipro.match.IdeaService;
+import se.su.dsv.scipro.match.Target;
+import se.su.dsv.scipro.match.TargetService;
+import se.su.dsv.scipro.system.User;
+import se.su.dsv.scipro.testdata.BaseData;
+import se.su.dsv.scipro.testdata.Factory;
+import se.su.dsv.scipro.testdata.TestDataPopulator;
+
+@Service
+public class PartnerTypeExemption implements TestDataPopulator {
+
+    private final ApplicationPeriodService applicationPeriodService;
+    private final IdeaService ideaService;
+    private final TargetService targetService;
+
+    @Inject
+    public PartnerTypeExemption(
+        ApplicationPeriodService applicationPeriodService,
+        IdeaService ideaService,
+        TargetService targetService
+    ) {
+        this.applicationPeriodService = applicationPeriodService;
+        this.ideaService = ideaService;
+        this.targetService = targetService;
+    }
+
+    @Override
+    public void populate(BaseData baseData, Factory factory) {
+        factory.createAuthor("Oskar");
+
+        User johan = factory.createAuthor("Johan");
+        johan.setDegreeType(baseData.master().getDegreeType());
+
+        User supervisor = factory.createSupervisor("Elsa");
+
+        ApplicationPeriod applicationPeriod = new ApplicationPeriod("Supervisor ideas");
+        applicationPeriod.setStartDate(LocalDate.now());
+        applicationPeriod.setEndDate(LocalDate.now().plusDays(14));
+        applicationPeriod.setCourseStartDateTime(LocalDateTime.now().plusDays(15));
+        applicationPeriod.setProjectTypes(Set.of(baseData.bachelor()));
+        applicationPeriodService.save(applicationPeriod);
+
+        Target target = targetService.findOne(applicationPeriod, supervisor, baseData.bachelor());
+        target.setTarget(10);
+        targetService.save(target);
+
+        Idea idea = new Idea();
+        idea.setPublished(true);
+        idea.setTitle("The next gen AI 2.0 turbo edition");
+        idea.setPrerequisites("Hacker experience");
+        idea.setDescription("Better than all the rest");
+        idea.setProjectType(baseData.bachelor());
+        idea.setApplicationPeriod(applicationPeriod);
+        idea.setResearchArea(baseData.researchArea().researchArea());
+
+        ideaService.saveSupervisorIdea(idea, supervisor, baseData.researchArea().keywords(), true);
+    }
+}

view/src/main/java/se/su/dsv/scipro/datatables/project/ProjectDataPanel.java

@@ -1,6 +1,5 @@
 package se.su.dsv.scipro.datatables.project;
 
-import com.google.common.eventbus.EventBus;
 import jakarta.inject.Inject;
 import java.util.*;
 import org.apache.wicket.ajax.AjaxRequestTarget;
@@ -33,7 +32,6 @@ import se.su.dsv.scipro.components.datatables.MultipleUsersColumn;
 import se.su.dsv.scipro.components.datatables.UserColumn;
 import se.su.dsv.scipro.dataproviders.FilteredDataProvider;
 import se.su.dsv.scipro.datatables.AjaxCheckboxWrapper;
-import se.su.dsv.scipro.notifications.NotificationController;
 import se.su.dsv.scipro.profile.UserLinkPanel;
 import se.su.dsv.scipro.project.Project;
 import se.su.dsv.scipro.project.ProjectService;
@@ -45,7 +43,6 @@ import se.su.dsv.scipro.system.ProjectType;
 import se.su.dsv.scipro.system.ProjectTypeService;
 import se.su.dsv.scipro.system.ResearchArea;
 import se.su.dsv.scipro.system.User;
-import se.su.dsv.scipro.system.UserService;
 import se.su.dsv.scipro.util.PageParameterKeys;
 
 public class ProjectDataPanel extends Panel {
@@ -170,6 +167,11 @@ public class ProjectDataPanel extends Panel {
             ) {
                 cellItem.add(new ReviewerColumnCell(componentId, rowModel));
             }
+
+            @Override
+            public IModel<?> getDataModel(IModel<Project> rowModel) {
+                return rowModel.map(Project::getReviewer).map(User::getFullName);
+            }
         };
     }
 

view/src/main/java/se/su/dsv/scipro/forum/ForumThread.java

@@ -10,4 +10,10 @@ public interface ForumThread<A> extends IClusterable {
     ForumPost reply(A a, User poster, String content, Set<Attachment> attachments);
     String getSubject(A a);
     void setRead(User user, A a);
+
+    default boolean canDelete(A a, ForumPost forumPost) {
+        return false;
+    }
+
+    default void deletePost(A a, ForumPost forumPost) {}
 }

view/src/main/java/se/su/dsv/scipro/forum/panels/threaded/ForumPostPanel.java

@@ -1,6 +1,5 @@
 package se.su.dsv.scipro.forum.panels.threaded;
 
-import jakarta.inject.Inject;
 import org.apache.wicket.Component;
 import org.apache.wicket.markup.html.WebMarkupContainer;
 import org.apache.wicket.markup.html.link.Link;
@@ -13,11 +12,9 @@ import se.su.dsv.scipro.components.ListAdapterModel;
 import se.su.dsv.scipro.components.SmarterLinkMultiLineLabel;
 import se.su.dsv.scipro.data.enums.DateStyle;
 import se.su.dsv.scipro.file.FileReference;
-import se.su.dsv.scipro.forum.BasicForumService;
 import se.su.dsv.scipro.forum.dataobjects.ForumPost;
 import se.su.dsv.scipro.profile.UserLinkPanel;
 import se.su.dsv.scipro.repository.panels.ViewAttachmentPanel;
-import se.su.dsv.scipro.session.SciProSession;
 
 public class ForumPostPanel extends Panel {
 
@@ -26,9 +23,6 @@ public class ForumPostPanel extends Panel {
     public static final String CONTENT = "content";
     public static final String ATTACHMENT = "attachment";
 
-    @Inject
-    private BasicForumService basicForumService;
-
     public ForumPostPanel(String id, final IModel<ForumPost> model) {
         super(id);
         add(new UserLinkPanel(POSTED_BY, LambdaModel.of(model, ForumPost::getPostedBy, ForumPost::setPostedBy)));
@@ -75,22 +69,23 @@ public class ForumPostPanel extends Panel {
                 @Override
                 public void onClick() {
                     ForumPost post = getModelObject();
-                    basicForumService.deletePost(post);
-                    onPostDeleted();
+                    deletePost(post).run();
                 }
 
                 @Override
                 protected void onConfigure() {
                     super.onConfigure();
-                    setVisible(allowDeletion() && basicForumService.canDelete(getModelObject()));
+                    setVisible(deletePost(getModelObject()) != null);
                 }
             }
         );
     }
 
-    protected boolean allowDeletion() {
-        return false;
+    /**
+     * @param forumPost the post to delete
+     * @return a runnable that deletes the post, or {@code null} if it can not be deleted
+     */
+    protected Runnable deletePost(ForumPost forumPost) {
+        return null;
     }
-
-    protected void onPostDeleted() {}
 }

view/src/main/java/se/su/dsv/scipro/forum/panels/threaded/ProjectForumThread.java

@@ -40,4 +40,14 @@ public class ProjectForumThread implements ForumThread<ProjectThread> {
     public void setRead(User user, ProjectThread thread) {
         projectForumService.markRead(user, thread);
     }
+
+    @Override
+    public boolean canDelete(ProjectThread projectThread, ForumPost forumPost) {
+        return projectForumService.canDelete(projectThread, forumPost);
+    }
+
+    @Override
+    public void deletePost(ProjectThread projectThread, ForumPost forumPost) {
+        projectForumService.deletePost(projectThread, forumPost);
+    }
 }

view/src/main/java/se/su/dsv/scipro/forum/panels/threaded/ViewForumThreadPanel.java

@@ -62,14 +62,16 @@ public class ViewForumThreadPanel<A> extends GenericPanel<A> {
                     item.add(
                         new ForumPostPanel(POST, item.getModel()) {
                             @Override
-                            protected boolean allowDeletion() {
-                                return true;
-                            }
-
-                            @Override
-                            protected void onPostDeleted() {
-                                // Refresh the list of posts
-                                listView.detach();
+                            protected Runnable deletePost(ForumPost forumPost) {
+                                if (forumThread.canDelete(ViewForumThreadPanel.this.getModelObject(), forumPost)) {
+                                    return () -> {
+                                        forumThread.deletePost(ViewForumThreadPanel.this.getModelObject(), forumPost);
+                                        // Refresh the list of posts
+                                        listView.detach();
+                                    };
+                                } else {
+                                    return null;
+                                }
                             }
                         }
                     );

view/src/main/java/se/su/dsv/scipro/group/EditGroupPanel.java

@@ -59,6 +59,11 @@ public class EditGroupPanel extends Panel {
             });
             add(
                 new ListView<>("available_projects", availableProjects) {
+                    {
+                        // must re-use list items to maintain form component (checkboxes) state
+                        setReuseItems(true);
+                    }
+
                     @Override
                     protected void populateItem(ListItem<Project> item) {
                         CheckBox checkbox = new CheckBox("selected", new SelectProjectModel(model, item.getModel()));

view/src/main/java/se/su/dsv/scipro/io/ExcelExporter.java

@@ -72,7 +72,9 @@ public class ExcelExporter extends AbstractDataExporter {
         for (int i = 0; i < columns.size(); i++) {
             Object cellValue = columns.get(i).getDataModel(data).getObject();
             Cell cell = row.createCell(i);
-            cell.setCellValue(String.valueOf(cellValue));
+            if (cellValue != null) {
+                cell.setCellValue(cellValue.toString());
+            }
         }
     }
 }