Automapper - Ignore mapping with condition

I'm using automapper and I would like to know if it's possible to ignore a mapping of a field when that's null.

That's my code:

.ForMember(dest => dest.BusinessGroup_Id, 
           opt => opt.MapFrom(src => (int)src.BusinessGroup))

• src.BusinessGroup type = "enum"
• dest.BusinessGroup_Id = int

The objective it's to ingore that Mapping if src.BusinessGroup = null.