bug: can not generate data type with 'string' #314

hello sir, i find a bug, when i define a data type using 'string' representation, ocarina raise error "Impossible to get the data size of this data", then i check the source code and find that when Data_Representation equals to Data_String, Value_Node was not updated in '../ocarina/src/backends/ast_c/ocarina-backends-c_tree-nutils.adb'. May be you can confirm whether it is a bug.

-- The example like this:
data person_name
properties
Data_Model::Data_Representation => string;
Data_Model::Dimension => (10);
end person_name;

subprogram print_a
features
port2: in parameter person_name;
end print_a;

and the source code like this:

 when Data_String | Data_Wide_String =>
 Value_UUL := Dimension (1);

Thanks for your reply!