Describe the bug
When given a yaml document of null goccy/yaml borks.

To Reproduce

https://go.dev/play/p/ZlT7pIhuQfd

Expected behavior
Should returns a ast.NullType node

Screenshots
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Version Variables

• Go version: [e.g. 1.21 ]
• go-yaml's Version: [e.g. v1.11.1 ]

Additional context
Add any other context about the problem here.