State machine InternalTransition question

Hi

Me again
In a state of a state machine, we can define several InternalTransition.
For each transition, we define the "Received event" (Do, Entry or Exit) and the "Expression of the action".
For the field "Expression of the action", Modelio suggest us the complete list of all available operations.
It is very good, but when we select one, we have just the operation without its parameters... without the possibility to enter some values for each parameter...
If i complete the field "Expression of the action" by adding myself some parameter's values, i lose the Operation type and it become a String type

exemple with operation printf(String text) :
1) just selecting printf() -> internalTransition.getProcessed() is not null, i get my operation (without parameter's value)
2) selecting printf() and adding "toto" inside brackets -> internalTransition.getProcessed() is null -> and i have "printf("toto")" in internalTransition.getEffect(), which is a String type... (very difficult to do the link with the concerned operation...)

My question his :
How can i define a complete InternalTransition action ?? By complete, i mean operation and values for its parameters
Is it possible ? or am i doomed to use the case 2) ?

Thanks by advance