maven-plugin-plugin:3.6.4:descriptor failed.: NullPointerException

Question

I had several inconsistencies in my pom so i tried to upgrade all versions, java to 11 and all plugins to the newest.

Now I have severe problem with maven-plugin-plugin:

[INFO] --- maven-plugin-plugin:3.6.4:descriptor (default-descriptor) @ latex-maven-plugin ---
[INFO] Using 'UTF-8' encoding to read mojo source files.
[INFO] java-javadoc mojo extractor found 0 mojo descriptor.
[INFO] bsh mojo extractor found 0 mojo descriptor.
[INFO] ant mojo extractor found 0 mojo descriptor.
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  15.423 s
[INFO] Finished at: 2022-03-03T02:49:06+01:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-site-plugin:3.9.1:site (default-site) on project latex-maven-plugin: failed to get report for org.apache.maven.plugins:maven-jxr-plugin: Failed to execute goal org.apache.maven.plugins:maven-plugin-plugin:3.6.4:descriptor (default-descriptor) on project latex-maven-plugin: Execution default-descriptor of goal org.apache.maven.plugins:maven-plugin-plugin:3.6.4:descriptor failed.: NullPointerException -> [Help 1]

In https://github.com/Reissner/maven-latex-plugin i pushed the latest working versions.

If I upgrade from java 8 to java 11 consistently, in compiler plugin, but leave the plugin-plugin version with the original 3.3 I obtain

[INFO] Applying mojo extractor for language: java-annotations
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  9.367 s
[INFO] Finished at: 2022-03-04T22:25:03+01:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-plugin-plugin:3.3:descriptor (default-descriptor) on project latex-maven-plugin: Execution default-descriptor of goal org.apache.maven.plugins:maven-plugin-plugin:3.3:descriptor failed.: IllegalArgumentException -> [Help 1]

Interesting enough, even if upgrading mockito causes problems with the plugin-plugin.

Also upgrading the plugin-plugin does not help. The only thing changing is the kind of exception thrown. So with maven-plugin-plugin 3.6.0 I obtain a nullpointer exception.

Caused by: java.lang.NullPointerException
    at org.apache.maven.tools.plugin.extractor.annotations.JavaAnnotationsMojoDescriptorExtractor.extractFieldParameterTags (JavaAnnotationsMojoDescriptorExtractor.java:405)
at org.apache.maven.tools.plugin.extractor.annotations.JavaAnnotationsMojoDescriptorExtractor.populateDataFromJavadoc (JavaAnnotationsMojoDescriptorExtractor.java:286)```

As i want a newer version for the plugin I tried hard to find out what's going wrong. 
Here is part of the stacktrace for 3.6.4: 

Caused by: java.lang.NullPointerException at org.apache.maven.tools.plugin.extractor.annotations.JavaAnnotationsMojoDescriptorExtractor.extractFieldParameterTags (JavaAnnotationsMojoDescriptorExtractor.java:408) at org.apache.maven.tools.plugin.extractor.annotations.JavaAnnotationsMojoDescriptorExtractor.populateDataFromJavadoc (JavaAnnotationsMojoDescriptorExtractor.java:280)

Note that the exceptions now come at a different place. 

I found the source I give below: 

private Map<String, JavaField>extractFieldParameterTags(JavaClass javaClass, Map<String, JavaClass> javaClassesMap) {
  try {
    Map<String, JavaField> rawParams = new TreeMap<>();

    // we have to add the parent fields first, so that they will be overwritten by the local fields if
    // that actually happens...
    JavaClass superClass = javaClass.getSuperJavaClass();

    if (superClass != null) {
      if (superClass.getFields().size() > 0) {
        rawParams = extractFieldParameterTags( superClass, javaClassesMap );
      }
      // maybe sources comes from scan of sources artifact
      superClass = javaClassesMap.get(superClass.getFullyQualifiedName());
      if (superClass != null) {
        rawParams = extractFieldParameterTags(superClass, javaClassesMap);
      }
    } else {
      rawParams = new TreeMap<>();
    }

    for (JavaField field : javaClass.getFields()) {
      rawParams.put(field.getName(), field); // <----- line 408
    }

    return rawParams;
  } catch (NoClassDefFoundError e) {
    getLogger().warn( "Failed extracting parameters from " + javaClass );
    throw e;
  }
}

I marked line 408 but cannot find a reason why this shall go wrong. 

Help very much appreciated.