Parser removing "#" in multiline strings

The following:

```
item:
  1:
    - value: |
        ### Header
```

Results in:

```
{
  "item": {
    "1": [
      {
        "value": ""
      }
    ]
  }
}
```

When it should result in:

```
{
  "item": {
    "1": [
      {
        "value": "### Header"
      }
    ]
  }
}
```