Apache Flink Dashboard not showing metrics

I have the following very simple Apache Flink Pipeline for which I would like to get some metrics, as explained in the Apache Flink documentation, via the Apache Flink Dashboard:

import org.apache.flink.api.common.functions.RichMapFunction;
import org.apache.flink.configuration.Configuration;
import org.apache.flink.metrics.Counter;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.streaming.api.functions.source.RichSourceFunction;

public class Pipeline {

    public static void main(String[] args) throws Exception {
        final StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();

        env.addSource(new RichSourceFunction<String>() {
            private static final long serialVersionUID = 3990963645875188158L;
            private boolean notCanceled = true;

            @Override
            public void run(SourceContext<String> ctx) throws Exception {
                while (notCanceled) {
                    ctx.collect("test");
                }
            }

            @Override
            public void cancel() {
                notCanceled = false;
            }
        }).map(new RichMapFunction<String, String>() {
            private static final long serialVersionUID = 1L;
            private transient Counter counter;

            @Override
            public void open(Configuration parameters) throws Exception {
                super.open(parameters);
                this.counter = getRuntimeContext()
                        .getMetricGroup()
                        .counter("myCounter");
            }

            @Override
            public String map(String value) throws Exception {
                this.counter.inc();
                return "mappedtext";
            }
        }).print();

        env.execute();
    }

}

I do run that Pipeline using the Docker Setup available via Docker-Hub. Everything uses Apache Flink 1.10.0. The Pipeline runs fine, but when I try to view my metric I only get:

Now I ask myself what am I doing wrong? Is there some configuration parameter I am missing or is this not the correct place to view that metric in the dashboard? Can someone please advise or at least point me to a resource, where I would get more information?