Probable bug: method that nullifies model

maven-api-impl/src/main/java/org/apache/maven/internal/impl/model/DefaultModelPathTranslator.java

@@ -94,7 +94,7 @@ private <T> List<T> map(List<T> resources, Function<T, T> mapper) {
  for (int i = 0; i < resources.size(); i++) {
  T resource = resources.get(i);
  T newResource = mapper.apply(resource);
- if (newResource != null) {
+ if (newResource != resource) {
  if (newResources == null) {
  newResources = new ArrayList<>(resources);
  }
@@ -105,18 +105,39 @@ private <T> List<T> map(List<T> resources, Function<T, T> mapper) {
  return newResources;
  }
 
+ /**
+ * Returns a resource with all properties identical to the given resource, except the paths
+ * which are resolved according the given {@code basedir}. If the paths are unchanged, then
+ * this method returns the previous instance.
+ *
+ * @param resource the resource to relocate, or {@code null}
+ * @param basedir the new base directory
+ * @return relocated resource, or {@code null} if the given resource was null
+ */
+ @SuppressWarnings("StringEquality") // Identity comparison is ok in this method.
  private Resource alignToBaseDirectory(Resource resource, Path basedir) {
  if (resource != null) {
- String newDir = alignToBaseDirectory(resource.getDirectory(), basedir);
- if (newDir != null) {
- return resource.withDirectory(newDir);
+ String oldDir = resource.getDirectory();
+ String newDir = alignToBaseDirectory(oldDir, basedir);
+ if (newDir != oldDir) {
+ return resource.with().directory(newDir).build();
  }
  }
  return resource;
  }
 
+ /**
+ * Returns a path relocated to the given base directory. If the result of this operation
+ * is the same path as before, then this method returns the old {@code path} instance.
+ * It is okay for the caller to compare the {@link String} instances using the identity
+ * comparator for detecting changes.
+ *
+ * @param path the path to relocate, or {@code null}
+ * @param basedir the new base directory
+ * @return relocated path, or {@code null} if the given path was null
+ */
  private String alignToBaseDirectory(String path, Path basedir) {
  String newPath = pathTranslator.alignToBaseDirectory(path, basedir);
- return Objects.equals(path, newPath) ? null : newPath;
+ return Objects.equals(path, newPath) ? path : newPath;
  }
 }

maven-model-builder/src/main/java/org/apache/maven/model/path/DefaultModelPathTranslator.java

@@ -116,7 +116,7 @@ private <T> List<T> map(List<T> resources, Function<T, T> mapper) {
 
  private Resource alignToBaseDirectory(Resource resource, Path basedir) {
  if (resource != null) {
- String newDir = alignToBaseDirectory(resource.getDirectory(), basedir);
+ String newDir = mayAlignToBaseDirectoryOrNull(resource.getDirectory(), basedir);
  if (newDir != null) {
  return resource.withDirectory(newDir);
  }
@@ -125,6 +125,17 @@ private Resource alignToBaseDirectory(Resource resource, Path basedir) {
  }
 
  private String alignToBaseDirectory(String path, Path basedir) {
+ String newPath = mayAlignToBaseDirectoryOrNull(path, basedir);
+ if (newPath != null) {
+ return newPath;
+ }
+ return path;
+ }
+
+ /**
+ * Returns aligned path or {@code null} if no need for change.
+ */
+ private String mayAlignToBaseDirectoryOrNull(String path, Path basedir) {
  String newPath = pathTranslator.alignToBaseDirectory(path, basedir);
  return Objects.equals(path, newPath) ? null : newPath;
  }