Convert integer to string in AJO ranking

Hello, I have a requirement where i have to get a dynamic value from the map, this map is stored on the profile of the customer. They key of this map has two components , one component that comes from context data and other component that comes from offer attribute, what i want to do is to append context data and offer attribute and fetch the value of this key from profile. The problem is when i use + to append them the + function always returns a double and hence i get an error that i can’t pass double as a key. I searched the documentation but there is no way to append two strings in AJO ranking. 

Does someone has any idea on how to fix this.