You can figure that out easily by inspecting the result data of an microflow invocation (which has an open form action) in firebug.
"MyFirstModule/entity_newedit.mxf", at least in 184.108.40.206, in which I am currently running a project
update Note that the formname is lowercased, but the module name not! (You might not note the difference when running locally, but when you deploy in the cloud, you need to get the casing right otherwise the forms won't show up. )
update I only used the API call version with a context, which did not give me a null pointer. Maybe substituting the third argument with 'null' will work around the exception.
this.addOpenFormFeedback(formname, FormTarget.WINDOW, mendixobject.getId(), new ArrayList<IMendixIdentifier>() );
I still get a Nullpointer Exception but there is no difference in case sensitive. Everything I try the exception comes but no form.
I got now a stacktrace:
Caused by: java.lang.NullPointerException at jm.<init>(SourceFile:23) at com.mendix.core.actionmanagement.CoreAction.addOpenFormFeedback (SourceFile:200) at com.mendix.core.actionmanagement.CoreAction.addOpenFormFeedback (SourceFile:188) at webblog.actions.OpenForm.executeAction (OpenForm.java:41) at webblog.actions.OpenForm.executeAction (OpenForm.java:1)