Not possible to retrieve process instances when using Container Alias

Issue

• There is a process container with container-id "TestContainer" and alias "TestAlias".
  When we call the "processes/instances/" REST API endpoint using the container-id this works:

$ curl --user "username:password" https://localhost:8080/kie-server/services/rest/server/containers/TestContainer/processes/instances/ 
    <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
    <process-instance-list>
        <process-instance>
            <process-instance-id>211</process-instance-id>
            <process-id>dsp.MainProcess</process-id>
            <process-name>MainProcess</process-name>
            <process-version>1.1</process-version>
            <process-instance-state>1</process-instance-state>
            <container-id>TestContainer</container-id>
            <initiator>anonymousUser</initiator>
            <start-date>2018-08-02T20:50:21.047+02:00</start-date>
            <process-instance-desc>MainProcess</process-instance-desc>
            <correlation-key>211</correlation-key>
            <parent-instance-id>-1</parent-instance-id>
        </process-instance>
    </process-instance-list>

However when we call the "processes/instances/" REST API endpoint using the container-alias this does not work:

$ curl --user "username:password" https://localhost:8080/kie-server/services/rest/server/containers/TestAlias/processes/instances/

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
    </process-instance-list>

Is this expected behaviour or a bug?