Resolves mojohaus#1197: Hande a no-version case in dependencyManageme…

…nt for CompareDependenciesMojo

- also resolve Maven 4 incompatibility of dummy-aggregate-*-333 artifacts in it-repo

versions-maven-plugin/src/main/java/org/codehaus/mojo/versions/CompareDependenciesMojo.java

@@ -26,6 +26,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 
 import org.apache.maven.artifact.Artifact;
 import org.apache.maven.artifact.handler.manager.ArtifactHandlerManager;
@@ -52,6 +53,7 @@
 import org.eclipse.aether.RepositorySystem;
 
 import static java.util.Collections.singletonList;
+import static java.util.Optional.ofNullable;
 
 /**
  * Compare dependency versions of the current project to dependencies or dependency management of a remote repository
@@ -296,7 +298,7 @@ private List<String> compareVersions(
             Dependency remoteDep = remoteDependencies.get(dep.getManagementKey());
             if (remoteDep != null) {
                 String remoteVersion = remoteDep.getVersion();
-                if (!dep.getVersion().equals(remoteVersion)) {
+                if (!Objects.equals(remoteVersion, dep.getVersion())) {
                     StringBuilder buf = writeDependencyDiffMessage(dep, remoteVersion);
                     updates.add(buf.toString());
                     if (!reportMode) {
@@ -414,7 +416,10 @@ private void writeReportFile(List<String> dependenciesUpdate, List<String> prope
      */
     private StringBuilder writeDependencyDiffMessage(Dependency dep, String remoteVersion) {
         String id = dep.getGroupId() + ":" + dep.getArtifactId();
-        return writeDiffMessage(id, dep.getVersion(), remoteVersion);
+        return writeDiffMessage(
+                id,
+                ofNullable(dep.getVersion()).orElse("(no version)"),
+                ofNullable(remoteVersion).orElse("(no version)"));
     }
 
     private StringBuilder writeDiffMessage(String id, String originalVersion, String targetVersion) {

versions-maven-plugin/src/test/java/org/codehaus/mojo/versions/CompareDependenciesMojoTest.java

@@ -0,0 +1,59 @@
+package org.codehaus.mojo.versions;
+
+import java.io.File;
+import java.util.Collections;
+
+import org.apache.maven.artifact.Artifact;
+import org.apache.maven.model.DependencyManagement;
+import org.apache.maven.model.Model;
+import org.apache.maven.plugin.testing.AbstractMojoTestCase;
+import org.apache.maven.plugin.testing.MojoRule;
+import org.apache.maven.project.MavenProject;
+import org.apache.maven.project.ProjectBuilder;
+import org.apache.maven.project.ProjectBuildingRequest;
+import org.apache.maven.project.ProjectBuildingResult;
+import org.codehaus.mojo.versions.utils.DependencyBuilder;
+import org.junit.Rule;
+import org.junit.Test;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyBoolean;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class CompareDependenciesMojoTest extends AbstractMojoTestCase {
+
+    @Rule
+    public final MojoRule mojoRule = new MojoRule(this);
+
+    @Test
+    public void testCompareVersionlessDependencies() throws Exception {
+        CompareDependenciesMojo mojo = (CompareDependenciesMojo) mojoRule.lookupConfiguredMojo(
+                new File("src/test/resources/org/codehaus/mojo/compare-dependencies/versionless"),
+                "compare-dependencies");
+        ProjectBuildingResult result = mock(ProjectBuildingResult.class);
+        when(result.getProblems()).thenReturn(Collections.emptyList());
+        when(result.getProject()).thenReturn(new MavenProject(new Model() {
+            {
+                setDependencyManagement(new DependencyManagement() {
+                    {
+                        setDependencies(Collections.singletonList(DependencyBuilder.newBuilder()
+                                .withGroupId("defaultGroup")
+                                .withArtifactId("artifactA")
+                                .withScope("test")
+                                .withVersion("1.0.0")
+                                .build()));
+                    }
+                });
+            }
+        }));
+
+        ProjectBuilder projectBuilder = mock(ProjectBuilder.class);
+        when(projectBuilder.build(any(Artifact.class), anyBoolean(), any(ProjectBuildingRequest.class)))
+                .thenReturn(result);
+        setVariableValueToObject(mojo, "projectBuilder", projectBuilder);
+        setVariableValueToObject(mojo, "remotePom", "defaultGroup:other-artifact:1.0.0");
+
+        mojo.execute();
+    }
+}

versions-maven-plugin/src/test/resources/org/codehaus/mojo/compare-dependencies/versionless/pom.xml

@@ -0,0 +1,18 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>default-group</groupId>
+  <artifactId>default-artifact</artifactId>
+  <version>1.0.0</version>
+
+  <dependencyManagement>
+    <dependencies>
+      <dependency>
+        <groupId>defaultGroup</groupId>
+        <artifactId>artifactA</artifactId>
+        <scope>test</scope>
+      </dependency>
+    </dependencies>
+  </dependencyManagement>
+
+</project>