Remove fails with type incompatibility with gson - Java 11

[Na3blis]

Description

Running a mvn clean with docker-maven-plugin configured with <removeNamePattern>${project.artifactId}:*</removeNamePattern> and

                            <execution>
                                <id>docker-remove</id>
                                <goals>
                                    <goal>remove</goal>
                                </goals>
                                <phase>clean</phase>
                            </execution>

causes the build to fail with the following error:
A type incompatibility occurred while executing io.fabric8:docker-maven-plugin:0.31.0:remove: class com.google.gson.JsonNull cannot be cast to class com.google.gson.JsonArray (com.google.gson.JsonNull and com.google.gson.JsonArray are in unnamed module of loader org.codehaus.plexus.classworlds.realm.ClassRealm

Info

• d-m-p version : .31 (also tried .33)
• Maven version (mvn -v) : 3.6.3
• Docker version : engine 19.03.8 - docker desktop 2.2.0.5
• If it's a bug, how to reproduce :
  Create a java 11 project with d-m-p setup to remove images on mvn clean. Untag an existing image so that it now displays none under tag. Run mvn clean
  NOTE
  This only started to happen when we updated to java 11, though one user had it occur on a java 8 project. It seems to be related to have an image tagged with none. If we manually delete any none tagged images, the issue goes away

[Na3blis]

PR fix for this #1355