Fix issues when reading/writing NULL values in YAML.

CHANGELOG.md

@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 - Fixed a bug that caused the `get` function to return `false` instead of an error when doing an invalid lookup.
+- Fixed an issue with reading/writing null values in YAML.
+- Fixed a nil pointer dereference when reading/writing null YAML documents.
 
 ## [v3.3.1] - 2026-02-26
 

parsing/yaml/yaml_reader.go

@@ -31,6 +31,12 @@ func (j *yamlReader) Read(data []byte) (*model.Value, error) {
 			}
 			return nil, err
 		}
+		if unmarshalled == nil {
+			unmarshalled = &yamlValue{
+				node:  nil,
+				value: model.NewNullValue(),
+			}
+		}
 		res = append(res, unmarshalled)
 	}
 
@@ -73,6 +79,10 @@ func (yv *yamlValue) UnmarshalYAML(value *yaml.Node) error {
 				return err
 			}
 			yv.value = model.NewFloatValue(f)
+		case "!!null":
+			yv.value = model.NewNullValue()
+		case "!!str":
+			yv.value = model.NewStringValue(value.Value)
 		default:
 			yv.value = model.NewStringValue(value.Value)
 		}

parsing/yaml/yaml_test.go

@@ -184,6 +184,20 @@ name2: *name
 `,
 		out: `name: Tom
 name2: Tom
+`,
+	}.run)
+
+	t.Run("null read write", rwTestCase{
+		in: `name: null
+`,
+		out: `name: null
+`,
+	}.run)
+
+	t.Run("null document read write", rwTestCase{
+		in: `null
+`,
+		out: `null
 `,
 	}.run)
 }

parsing/yaml/yaml_writer.go

@@ -2,6 +2,7 @@ package yaml
 
 import (
 	"fmt"
+
 	"github.com/tomwright/dasel/v3/model"
 	"github.com/tomwright/dasel/v3/parsing"
 	"go.yaml.in/yaml/v4"
@@ -109,7 +110,9 @@ func (yv *yamlValue) ToNode() (*yaml.Node, error) {
 			return nil, err
 		}
 	case model.TypeNull:
-		res.Kind = yaml.DocumentNode
+		res.Kind = yaml.ScalarNode
+		res.Value = "null"
+		res.Tag = "!!null"
 	case model.TypeUnknown:
 		return nil, fmt.Errorf("unknown type: %s", yv.value.Type())
 	}