Example
m := make(map[string][]int)
Accessing a non-existent key will return a nil slice as a value. Since nil slices act like zero length slices when used with append or other built-in functions you do not normally need to check to see if a key exists:
// m["key1"] == nil && len(m["key1"]) == 0
m["key1"] = append(m["key1"], 1)
// len(m["key1"]) == 1
Deleting a key from map sets the key back to a nil slice:
delete(m, "key1")
// m["key1"] == nil
