I use an extension method for this. My extension method first checks to see if the enumeration is null and if so creates an empty list. This allows you to do a foreach on it without explicitly having to check for null.
Here is a very contrived example:
IEnumerable<string> stringEnumerable = null;
StringBuilder csv = new StringBuilder();
stringEnumerable.ToNonNullList().ForEach(str=> csv.Append(str).Append(","));
Here is the extension method:
public static List<T> ToNonNullList<T>(this IEnumerable<T> obj)
{
return obj == null ? new List<T>() : obj.ToList();
}