fix(output): omit nulls from YAML output

internal/pkg/formatter/yaml.go

@@ -1,6 +1,7 @@
 package formatter
 
 import (
+	"encoding/json"
 	"fmt"
 	"regexp"
 	"strings"
@@ -56,7 +57,19 @@ func newYamlSerializer() *yamlSerializer {
 }
 
 func (s *yamlSerializer) serialize(v any, colored bool) (string, error) {
-	b, err := yaml.Marshal(v)
+	// there isn't really a good way to drop null values from YAML,
+	// so we pass it through the JSON marshaller first
+	jsonBytes, err := json.Marshal(v)
+	if err != nil {
+		return "", err
+	}
+
+	var cleaned any
+	if err := json.Unmarshal(jsonBytes, &cleaned); err != nil {
+		return "", err
+	}
+
+	b, err := yaml.Marshal(cleaned)
 	if err != nil {
 		return "", err
 	}

internal/pkg/formatter/yaml_test.go

@@ -8,6 +8,22 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+// dummyStruct is a test struct with omitempty tags to verify null values are dropped
+type dummyStruct struct {
+	Name   string        `json:"name"`
+	Age    int           `json:"age"`
+	Email  *string       `json:"email,omitempty"`
+	Phone  *string       `json:"phone,omitempty"`
+	Active bool          `json:"active"`
+	Score  *int          `json:"score,omitempty"`
+	Nested *nestedStruct `json:"nested,omitempty"`
+}
+
+type nestedStruct struct {
+	Value    string  `json:"value"`
+	Optional *string `json:"optional,omitempty"`
+}
+
 func TestPrintYAML_TableDriven(t *testing.T) {
 	tests := []struct {
 		name     string
@@ -97,3 +113,104 @@ negative: -10
 		})
 	}
 }
+
+func TestYamlSerializer_serialize_DropsNullValuesWithOmitempty(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    any
+		colored  bool
+		expected string
+	}{
+		{
+			name: "drops null pointer fields with omitempty",
+			input: dummyStruct{
+				Name:   "Alice",
+				Age:    30,
+				Email:  nil, // Should be dropped
+				Phone:  nil, // Should be dropped
+				Active: true,
+				Score:  nil, // Should be dropped
+			},
+			colored: false,
+			expected: `active: true
+age: 30
+name: Alice
+`,
+		},
+		{
+			name: "keeps non-null pointer fields with omitempty",
+			input: dummyStruct{
+				Name:   "Bob",
+				Age:    25,
+				Email:  stringPtr("bob@example.com"),
+				Phone:  nil, // Should be dropped
+				Active: false,
+				Score:  intPtr(100),
+			},
+			colored: false,
+			expected: `active: false
+age: 25
+email: bob@example.com
+name: Bob
+score: 100
+`,
+		},
+		{
+			name: "drops nested struct with omitempty when nil",
+			input: dummyStruct{
+				Name:   "Charlie",
+				Age:    35,
+				Email:  stringPtr("charlie@example.com"),
+				Active: false,
+				Nested: nil, // Should be dropped
+			},
+			colored: false,
+			expected: `active: false
+age: 35
+email: charlie@example.com
+name: Charlie
+`,
+		},
+		{
+			name: "keeps nested struct with omitempty when not nil",
+			input: dummyStruct{
+				Name:   "David",
+				Age:    40,
+				Email:  stringPtr("david@example.com"),
+				Active: false,
+				Nested: &nestedStruct{
+					Value:    "test",
+					Optional: nil, // Should be dropped from nested struct
+				},
+			},
+			colored: false,
+			expected: `active: false
+age: 40
+email: david@example.com
+name: David
+nested:
+    value: test
+`,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			serializer := newYamlSerializer()
+			result, err := serializer.serialize(tt.input, tt.colored)
+			require.NoError(t, err)
+
+			assert.Equal(t, tt.expected, result)
+			// Verify that "null" doesn't appear in the output
+			assert.NotContains(t, result, "null")
+		})
+	}
+}
+
+func stringPtr(s string) *string {
+	return &s
+}
+
+func intPtr(i int) *int {
+	return &i
+}