Persist HashMap<Integer,HashMap<String,String>>

Hi,

I have a project service implementing the PersistentStateComponent interface.

Everything works fine for simple types of values, such as HashMap<Integer,String> etc.

But now I need to persist something like HashMap<Integer,HashMap<String,String>> 

How can I do that?

The problem is that in the xml file the value of the first map has the entry HashMap but this map is always empty