A flow mapping entry may omit its `:` value indicator, in which case its key
maps to null: `{ a }` and `{ a, b }` are flow sets. parseFlowMappingPair
required a `:` after every key, so it rejected these entries, and rejected a
valueless key that spanned lines (`{ multi\n line, a: b}`) with them.
Parse a value only when a `:` follows the key; otherwise emit a null value for
the key. A unit test that asserted `{ a, }` was an error is corrected to expect
the set `{a: null}`, the behaviour the yaml-test-suite cases 8KB6 and 9BXH
require.
Raises yaml-test-suite parse-level conformance to 304/333 (91.3%) and
value-level to 195/197, with the should-error rejection rate unchanged.
480 tests pass.
Mihaela M
31da488055