A ':' value indicator with no preceding key on its line denotes a
mapping entry whose key is empty (null), which YAML 1.2 permits but
libyaml rejects with 'did not find expected key'. The block-mapping-key
parser now emits the empty scalar key and leaves the VALUE token for the
value state to consume, rather than throwing.
Fixes the canonical event streams for plain empty-key mappings, explicit
empty keys with anchors and aliases, empty keys nested in sequences, and
mixed empty-key/value entries. Port score 275 -> 282; surpasses libyaml
on 2JQS, 6M2F, M2N8/00, NHX8, S3PD, SM9W/01, UKK6/00.
Mihaela Mihaljevic
70c3da85a3