Describe the bug
For an empty multi line input like |- is getting replace with ''

To Reproduce
Steps to reproduce the behaviour.

When parsing a YAML document containing an empty block scalar using |- (block literal).
Then serializing it back with .toString(), the scalar is converted to a plain quoted string ('').
Losing its original formatting.

Input YAML
input: |-

Output YAML
input: ''

Expected behaviour
A clear and concise description of what you expected to happen.

Input YAML

input: |-

Output YAML

input: |-

Versions (please complete the following information):

• Environment:
• Node.js 22.14.0
• yaml: 2.6.1

Additional context
Add any other context about the problem here.