NullPointerException when annotating com.google.cloud:spring-cloud-gcp-dependencies

While checking takari-local-repository, I found NullPointerException (memo). Even with the latest 1.5.4 Linkage Checker enforcer rule, the problem (https://github.com/GoogleCloudPlatform/cloud-opensource-java/issues/1609) recurs

suztomo@suztomo:~/spring-cloud-gcp$ mvn  --activate-profiles linkage-check\
             --batch-mode --show-version\
             --threads 1.5C --define skipTests=true\
             --define maven.javadoc.skip=true  --errors install

...

suztomo@suztomo:~/spring-cloud-gcp$ git remote -v
origin	https://github.com/GoogleCloudPlatform/spring-cloud-gcp.git (fetch)
origin	https://github.com/GoogleCloudPlatform/spring-cloud-gcp.git (push)
suztomo@suztomo:~/spring-cloud-gcp$ git diff
diff --git a/spring-cloud-gcp-dependencies/pom.xml b/spring-cloud-gcp-dependencies/pom.xml
index b0752ca0..2050a6d8 100644
--- a/spring-cloud-gcp-dependencies/pom.xml
+++ b/spring-cloud-gcp-dependencies/pom.xml
@@ -370,7 +370,7 @@
                                                        <dependency>
                                                                <groupId>com.google.cloud.tools</groupId>
                                                                <artifactId>linkage-checker-enforcer-rules</artifactId>
-                                                               <version>1.5.3</version>
+                                                               <version>1.5.4</version>
                                                        </dependency>
                                                </dependencies>
                                                <executions>




[INFO] Spring Cloud GCP Dependencies ...................... FAILURE [03:58 min]
[INFO] Spring Cloud GCP Documentation ..................... SUCCESS [  5.141 s]
[INFO] Spring Cloud GCP Code Samples ...................... SUCCESS [  6.414 s]
[INFO] Spring Cloud GCP Code Sample - Runtime Configuration SUCCESS [  0.863 s]
[INFO] Spring Cloud GCP Code Sample - Trace ............... SUCCESS [  1.134 s]
[INFO] Spring Cloud GCP Code Sample - Logging ............. SUCCESS [  5.685 s]
[INFO] Spring Cloud GCP Code Sample - MySQL ............... SUCCESS [  0.901 s]
[INFO] Spring Cloud GCP Code Sample - Spring Integration Pub/Sub Channel Adapters SUCCESS [  1.726 s]
[INFO] Spring Cloud GCP Code Sample - Spring Integration Pub/Sub Sender SUCCESS [  6.948 s]
[INFO] Spring Cloud GCP Code Sample - Spring Integration Pub/Sub Receiver SUCCESS [  3.521 s]
[INFO] Spring Cloud GCP Code Sample - Spring Integration Pub/Sub Polling Receiver SUCCESS [  0.939 s]
[INFO] Spring Cloud GCP Code Sample - Spring Integration Pub/Sub Integration Test SUCCESS [  1.256 s]
[INFO] Spring Cloud GCP Code Sample - Storage ............. SUCCESS [  4.935 s]
[INFO] Spring Cloud GCP Code Sample - Spanner ............. SUCCESS [  6.570 s]
[INFO] Spring Cloud GCP Code Sample - Datastore ........... SUCCESS [  1.401 s]
[INFO] Spring Cloud GCP Code Sample - Datastore Bookshelf . SUCCESS [  1.170 s]
[INFO] Spring Cloud GCP Code Sample - Pub/Sub ............. SUCCESS [  5.817 s]
[INFO] Spring Cloud GCP Code Sample - Spring Data JPA ..... SUCCESS [  5.201 s]
[INFO] Spring Cloud GCP Code Sample - Vision API .......... SUCCESS [  1.230 s]
[INFO] Spring Cloud GCP Code Sample - Spring Integration Storage SUCCESS [  5.742 s]
[INFO] Spring Cloud GCP Code Sample - Pub/Sub Stream ...... SUCCESS [  2.143 s]
[INFO] Spring Cloud GCP Code Sample - Pub/Sub Bus Configuration Management SUCCESS [  1.725 s]
[INFO] Spring Cloud GCP Code Sample - Pub/Sub Bus (Client)  SUCCESS [  1.453 s]
[INFO] Spring Cloud GCP Code Sample - Spring Cloud Config with Pub/Sub Bus (Local Configuration) SUCCESS [  1.453 s]
[INFO] Spring Cloud GCP Code Sample - Spring Cloud Config with Pub/Sub Bus (GitHub Configuration) SUCCESS [  1.452 s]
[INFO] Spring Cloud GCP Code Sample - Spring Cloud Config with Pub/Sub Bus Integration Test SUCCESS [  1.620 s]
[INFO] Spring Cloud GCP Code Sample - Pub/Sub Stream Binder Polling SUCCESS [  2.143 s]
[INFO] Spring Cloud GCP Code Sample - Pub/Sub Reactive .... SUCCESS [  6.643 s]
[INFO] Spring Cloud GCP Code Sample - Spring Integration Pub/Sub JSON Payloads SUCCESS [  6.803 s]
[INFO] Spring Cloud GCP Code Sample - IAP ................. SUCCESS [  0.873 s]
[INFO] Spring Cloud GCP Code Sample - Postgres ............ SUCCESS [  6.156 s]
[INFO] Spring Cloud GCP Code Sample - Vision OCR .......... SUCCESS [  5.332 s]
[INFO] Spring Cloud GCP Code Sample - Firestore ........... SUCCESS [  0.968 s]
[INFO] Spring Cloud GCP Code Sample - Multi-Spring-Data-Module SUCCESS [  1.103 s]
[INFO] Spring Cloud GCP Code Sample - Spring Data Firestore SUCCESS [  6.507 s]
[INFO] Spring Cloud GCP Code Sample - BigQuery ............ SUCCESS [  6.511 s]
[INFO] Spring Cloud GCP Code Sample - Pub/Sub Stream Binder (Functional style) SUCCESS [  1.713 s]
[INFO] Spring Cloud GCP Code Sample - Pub/Sub Stream Binder Source SUCCESS [  2.191 s]
[INFO] Spring Cloud GCP Code Sample - Pub/Sub Stream Binder Sink SUCCESS [  2.191 s]
[INFO] Spring Cloud GCP Code Sample - Pub/Sub Stream Binder Integration Test SUCCESS [  1.465 s]
[INFO] Spring Cloud GCP Code Sample - Firebase Security ... SUCCESS [  5.542 s]
[INFO] Spring Cloud GCP Code Sample - Secret Manager ...... SUCCESS [  1.358 s]
[INFO] Spring Cloud GCP Code Samples - Kotlin ............. SUCCESS [  1.732 s]
[INFO] Spring Cloud GCP Code Sample - Kotlin App Sample ... SUCCESS [ 14.329 s]
[INFO] Spring Cloud GCP Code Sample - Metrics ............. SUCCESS [  0.934 s]
[INFO] Spring Cloud GCP Code Sample - KMS ................. SUCCESS [  1.068 s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  04:00 min (Wall Clock)
[INFO] Finished at: 2020-12-29T22:06:59Z
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-enforcer-plugin:3.0.0-M3:enforce (enforce-linkage-checker) on project spring-cloud-gcp-dependencies: Execution enforce-linkage-checker of goal org.apache.maven.plugins:maven-enforcer-plugin:3.0.0-M3:enforce failed. NullPointerException -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-enforcer-plugin:3.0.0-M3:enforce (enforce-linkage-checker) on project spring-cloud-gcp-dependencies: Execution enforce-linkage-checker of goal org.apache.maven.plugins:maven-enforcer-plugin:3.0.0-M3:enforce failed.
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:215)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:190)
    at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:186)
    at java.util.concurrent.FutureTask.run (FutureTask.java:266)
    at java.util.concurrent.Executors$RunnableAdapter.call (Executors.java:511)
    at java.util.concurrent.FutureTask.run (FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:624)
    at java.lang.Thread.run (Thread.java:748)
Caused by: org.apache.maven.plugin.PluginExecutionException: Execution enforce-linkage-checker of goal org.apache.maven.plugins:maven-enforcer-plugin:3.0.0-M3:enforce failed.
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:148)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:190)
    at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:186)
    at java.util.concurrent.FutureTask.run (FutureTask.java:266)
    at java.util.concurrent.Executors$RunnableAdapter.call (Executors.java:511)
    at java.util.concurrent.FutureTask.run (FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:624)
    at java.lang.Thread.run (Thread.java:748)
Caused by: java.lang.NullPointerException
    at com.google.cloud.tools.opensource.dependencies.DependencyGraph.levelOrder (DependencyGraph.java:259)
    at com.google.cloud.tools.opensource.dependencies.DependencyGraph.from (DependencyGraph.java:244)
    at com.google.cloud.tools.opensource.dependencies.DependencyGraphBuilder.buildDependencyGraph (DependencyGraphBuilder.java:209)
    at com.google.cloud.tools.opensource.dependencies.DependencyGraphBuilder.buildMavenDependencyGraph (DependencyGraphBuilder.java:198)
    at com.google.cloud.tools.opensource.classpath.ClassPathBuilder.resolveWithMaven (ClassPathBuilder.java:80)
    at com.google.cloud.tools.opensource.classpath.LinkageProblemCauseAnnotator.annotate (LinkageProblemCauseAnnotator.java:59)
    at com.google.cloud.tools.dependencies.enforcer.LinkageCheckerRule.execute (LinkageCheckerRule.java:223)
    at org.apache.maven.plugins.enforcer.EnforceMojo.execute (EnforceMojo.java:205)
...

As per the stacktrace Linkage Checker was trying to annotate linkage errors (LinkageProblemCauseAnnotator.annotate).

Note that this happens without using takari local repository extension.