D slices can be null, but they're not a mistake, as the runtime will not let you read/write a 0 length array.
"var x []int; fmt.Printf(`%p %d`, x, len(x))" outputs "0x0 0"
Indexing "x[0]" results in: "panic: runtime error: index out of range [0] with length 0"
They can also be appended to and then produce a valid slice.