Error when updating Wiki: Entity may not be null

[kuruhuru]

I created a simple test that leads to an error on Redmine 4.1.0.stable

    public static void main(String[] args) {
        RedmineManager manager = RedmineManagerFactory.createWithApiKey("XXX",
                "XXX");
        Transport transport = manager.getTransport();
        ProjectManager projectManager = manager.getProjectManager();
        try {
            Project project = projectManager.getProjectByKey("secs-building-example-project");
            WikiPageDetail wdetail = manager.getWikiManager().getWikiPageDetailByProjectAndTitle(
                    "secs-building-example-project", "Wiki");
            wdetail.setText(wdetail.getText() + "\nCHANGED!!!");
            wdetail.update();
        } catch (RedmineException) {
            e.printStackTrace();
        }
    }

Exception in thread "main" java.lang.IllegalArgumentException: Entity may not be null
	at org.apache.http.util.Args.notNull(Args.java:54)
	at org.apache.http.util.EntityUtils.getContentCharSet(EntityUtils.java:159)
	at com.taskadapter.redmineapi.internal.comm.HttpUtil.getCharset(HttpUtil.java:32)
	at com.taskadapter.redmineapi.internal.comm.TransportDecoder.processContent(TransportDecoder.java:26)
	at com.taskadapter.redmineapi.internal.comm.TransportDecoder.processContent(TransportDecoder.java:19)
	at com.taskadapter.redmineapi.internal.comm.ComposingHandler.processContent(ComposingHandler.java:25)
	at com.taskadapter.redmineapi.internal.comm.ComposingHandler.processContent(ComposingHandler.java:25)
	at com.taskadapter.redmineapi.internal.comm.BaseCommunicator.sendRequest(BaseCommunicator.java:47)
	at com.taskadapter.redmineapi.internal.comm.redmine.RedmineAuthenticator.sendRequest(RedmineAuthenticator.java:52)
	at com.taskadapter.redmineapi.internal.comm.FmapCommunicator.sendRequest(FmapCommunicator.java:26)
	at com.taskadapter.redmineapi.internal.comm.FmapCommunicator.sendRequest(FmapCommunicator.java:26)
	at com.taskadapter.redmineapi.internal.comm.BasicSimplifier.sendRequest(BasicSimplifier.java:24)
	at com.taskadapter.redmineapi.internal.Transport.send(Transport.java:605)
	at com.taskadapter.redmineapi.internal.Transport.updateChildEntry(Transport.java:297)
	at com.taskadapter.redmineapi.bean.WikiPageDetail.update(WikiPageDetail.java:142)
	at org.example.redmine.RedmineTest.main(RedmineTest.java:30)

Execution failed for task ':RedmineTest.main()'.
> Process 'command '/usr/lib/jvm/java-1.14.0-openjdk-amd64/bin/java'' finished with non-zero exit value 1

[haiyanghaiyang]

I've created a PR: #355
I don't know how to run the test. But I got it works with Gerrit its-redmine plugin with Redmine 4.1.1. Please have a try.