Describe the bug

null as a key is parsed as the empty string:

> yaml.parse('null: 1')
{ '': 1 }

To Reproduce

> yaml.parse('null: 1')
{ '': 1 }

Expected behaviour

> yaml.parse('null: 1')
{ 'null': 1 }

Versions (please complete the following information):

• Environment: node 20.x
• yaml: "2.4.3"

Additional context

• https://yaml.org/spec/1.2.2/#10211-null
• also, see header "Example 2.21 Miscellaneous"