diff --git a/api/maven-api-core/src/main/java/org/apache/maven/api/Project.java b/api/maven-api-core/src/main/java/org/apache/maven/api/Project.java
index 47342ce8a7ec..219e21f2469b 100644
--- a/api/maven-api-core/src/main/java/org/apache/maven/api/Project.java
+++ b/api/maven-api-core/src/main/java/org/apache/maven/api/Project.java
@@ -224,6 +224,13 @@ default String getId() {
 
     /**
      * Returns project parent project, if any.
+     * <p>
+     * Note that the model may have a parent defined, but an empty parent
+     * project may be returned if the parent comes from a remote repository,
+     * as a {@code Project} must refer to a buildable project.
+     *
+     * @return an optional containing the parent project
+     * @see Model#getParent()
      */
     @Nonnull
     Optional<Project> getParent();
diff --git a/maven-api-impl/src/main/java/org/apache/maven/internal/impl/Utils.java b/maven-api-impl/src/main/java/org/apache/maven/internal/impl/Utils.java
index 0d0d43c32f93..2fb4ad3d338c 100644
--- a/maven-api-impl/src/main/java/org/apache/maven/internal/impl/Utils.java
+++ b/maven-api-impl/src/main/java/org/apache/maven/internal/impl/Utils.java
@@ -20,6 +20,7 @@
 
 import java.util.Collection;
 import java.util.List;
+import java.util.Objects;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 
@@ -49,6 +50,6 @@ static <T> T cast(Class<T> clazz, Object o, String name) {
     }
 
     static <U, V> List<V> map(Collection<U> list, Function<U, V> mapper) {
-        return list.stream().map(mapper).collect(Collectors.toList());
+        return list.stream().map(mapper).filter(Objects::nonNull).collect(Collectors.toList());
     }
 }
diff --git a/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultEvent.java b/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultEvent.java
index 2f4cf648c832..2f03e6654333 100644
--- a/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultEvent.java
+++ b/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultEvent.java
@@ -48,7 +48,7 @@ public Session getSession() {
 
     @Override
     public Optional<Project> getProject() {
-        return Optional.ofNullable(delegate.getProject()).map(session::getProject);
+        return Optional.ofNullable(session.getProject(delegate.getProject()));
     }
 
     @Override
diff --git a/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultProject.java b/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultProject.java
index ba1c6d708fc8..359f84094a12 100644
--- a/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultProject.java
+++ b/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultProject.java
@@ -159,7 +159,7 @@ public Path getRootDirectory() {
     @Override
     public Optional<Project> getParent() {
         MavenProject parent = project.getParent();
-        return parent != null ? Optional.of(session.getProject(parent)) : Optional.empty();
+        return Optional.ofNullable(session.getProject(parent));
     }
 
     @Nonnull
diff --git a/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultProjectBuilder.java b/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultProjectBuilder.java
index a446f63b26ee..efc6d3e7855a 100644
--- a/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultProjectBuilder.java
+++ b/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultProjectBuilder.java
@@ -100,7 +100,7 @@ public Optional<Path> getPomFile() {
                 @Nonnull
                 @Override
                 public Optional<Project> getProject() {
-                    return Optional.ofNullable(res.getProject()).map(session::getProject);
+                    return Optional.ofNullable(session.getProject(res.getProject()));
                 }
 
                 @Nonnull
diff --git a/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultSession.java b/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultSession.java
index cd83f7c44921..a931b9874ba7 100644
--- a/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultSession.java
+++ b/maven-core/src/main/java/org/apache/maven/internal/impl/DefaultSession.java
@@ -93,7 +93,9 @@ public List<Project> getProjects(List<MavenProject> projects) {
 
     @Override
     public Project getProject(MavenProject project) {
-        return allProjects.computeIfAbsent(project.getId(), id -> new DefaultProject(this, project));
+        return project != null && project.getBasedir() != null
+                ? allProjects.computeIfAbsent(project.getId(), id -> new DefaultProject(this, project))
+                : null;
     }
 
     @Override
diff --git a/maven-core/src/main/java/org/apache/maven/internal/impl/InternalMavenSession.java b/maven-core/src/main/java/org/apache/maven/internal/impl/InternalMavenSession.java
index 1ee399c6c040..4df67943e8ea 100644
--- a/maven-core/src/main/java/org/apache/maven/internal/impl/InternalMavenSession.java
+++ b/maven-core/src/main/java/org/apache/maven/internal/impl/InternalMavenSession.java
@@ -23,6 +23,7 @@
 import org.apache.maven.api.Project;
 import org.apache.maven.api.RemoteRepository;
 import org.apache.maven.api.Session;
+import org.apache.maven.api.annotations.Nullable;
 import org.apache.maven.execution.MavenSession;
 
 import static org.apache.maven.internal.impl.Utils.cast;
@@ -35,6 +36,10 @@ static InternalMavenSession from(Session session) {
 
     List<Project> getProjects(List<org.apache.maven.project.MavenProject> projects);
 
+    /**
+     * May return null if the input projcet is null or is not part of the reactor.
+     */
+    @Nullable
     Project getProject(org.apache.maven.project.MavenProject project);
 
     List<org.apache.maven.artifact.repository.ArtifactRepository> toArtifactRepositories(
diff --git a/maven-core/src/main/java/org/apache/maven/project/DefaultProjectBuilder.java b/maven-core/src/main/java/org/apache/maven/project/DefaultProjectBuilder.java
index f840bc4dbb8a..4c8c9080dc0b 100644
--- a/maven-core/src/main/java/org/apache/maven/project/DefaultProjectBuilder.java
+++ b/maven-core/src/main/java/org/apache/maven/project/DefaultProjectBuilder.java
@@ -692,7 +692,9 @@ private InterimResult build(
             // In case the model is using CI friendly versions, at this point, it will contain uninterpolated version
             // such as ${revision}${changelist}, so we need to take care of it now
             Model modelWithVersion = getModelWithInterpolatedVersion(model, result.getProblems()::add);
-            modelPool.put(model.getPomFile(), modelWithVersion);
+            if (model.getPomFile() != null) {
+                modelPool.put(model.getPomFile(), modelWithVersion);
+            }
 
             InterimResult interimResult = new InterimResult(pomFile, modelBuildingRequest, result, project, isRoot);