1# A document may be null.
2---
3---
4# This mapping has four keys,
5# one has a value.
6empty:
7canonical: ~
8english: null
9~: null key
10---
11# This sequence has five
12# entries, two have values.
13sparse:
14 - ~
15 - 2nd entry
16 -
17 - 4th entry
18 - Null
19