C# add new element to list
- C# add element to list
- C# add element to list first position
- C# add element to list at index
- C# add element to list string
- C# add class element to list
- C# add element to list if not exists
- C# add element to list only if not exists
- C# add element to list if not null
- C# add element to list and return
- C# add empty element to list