Help with ACL to restrict next state

[aph]

In my setup, there are activity dialogs which contain some must fields. However, agents often forget to fill out these must fields before closing the ticket. Is there a way to prevent agents from closing tickets before filling in must fields?
The possibility to add these fields to AgentTicketClose dialog as must fields in not viable as the fields differ from process to process. As another way I thought I could use ACLs to restrict the next possible states in the close dialog. My ACL is as follows:

Unbenannt_168.PNG

I was hoping to restrict the next state for the ticket so the list will be empty. Apart from the fact that the given ACL does not work, I realized that I cannot make the field next state in close dialog mandatory via sysconfig, so having an empty drop down of next possible states could have an adverse effect.

Does anyone have an idea how I can implement the given functionality so that a ticket cannot be closed before the mandatory fields in the activity dialogue are filled

[aph]

Following this thread viewtopic.php?t=20749#p82168 I tried to hide the 'close' button, so that an agent is complelled to open the activity dialog in order to close the ticket. But the option Action is not visible under 'PossibleNot' for me.

Unbenannt_172.PNG

Any pointers?

[aph]

EDIT: Found out had to unclick the value under possible actions.

[aph]

I'm trying a slightly different approach here. I would like to hide the close button alltogether, if a mandatory field in the activity dialog is empty. I have added an 'empty' value to drop down field and set it as default. But somehow I'm not able to get the ACL working. Below is my ACL:

Unbenannt_178.PNG

I also tried using match property DynamicField -> DynamicField_Kategorie yet no luck
Where am I going wrong? Any pointers?

[aph]

As it appears, although the default value for the drop down field is shown in the activity dialog, it does not become effective until I click the submit button. To get around this, I set the default value using a generic agent at TicketCreate event.After this the ACL works