`map` parsed as `string`

[RedCMD]

Describe the bug
a flow map with an empty value should be parsed as map, not string
Flow nodes and flow keys are not allowed to contain the character set :]

To Reproduce

[a:b]
---
[c:]
---
[:]
---
a:b
---
c:
---
:

Expected behaviour
[c:] should be a map with c key and empty for the value
[a:b] is correctly parsed as a string
[:] is correctly parsed as an empty map

Versions:

• Environment: VSCode 1.89
• yaml: 2.4.3

Additional context

[eemeli]

[c:] should be a map with c key and empty for the value

Agreed, there's something wrong in the ns-plain-char lookahead, which should recognise the ] after the : as a c-flow-indicator, so that this parses the same as [c:,] or [c: ].

[:] is correctly parsed as an empty map

To be picky, it's a sequence with a map as a value, and that map has a single pair with empty key and value. But it is indeed correctly parsed.