diff --git a/pkg/types/binary.go b/pkg/types/binary.go
index 00a5417f..9fb0a9f4 100644
--- a/pkg/types/binary.go
+++ b/pkg/types/binary.go
@@ -65,7 +65,7 @@ func (binary *Binary) UnmarshalText(text []byte) error {
 // Supports JSON null.
 func (binary Binary) MarshalJSON() ([]byte, error) {
 	if !binary.Valid() {
-		return nil, nil
+		return []byte("null"), nil
 	}
 
 	return internal.MarshalJSON(binary.String())
diff --git a/pkg/types/binary_test.go b/pkg/types/binary_test.go
new file mode 100644
index 00000000..2a4f8292
--- /dev/null
+++ b/pkg/types/binary_test.go
@@ -0,0 +1,29 @@
+package types
+
+import (
+	"github.com/stretchr/testify/require"
+	"testing"
+	"unicode/utf8"
+)
+
+func TestBinary_MarshalJSON(t *testing.T) {
+	subtests := []struct {
+		name   string
+		input  Binary
+		output string
+	}{
+		{"nil", nil, `null`},
+		{"empty", make(Binary, 0, 1), `null`},
+		{"space", Binary(" "), `"20"`},
+	}
+
+	for _, st := range subtests {
+		t.Run(st.name, func(t *testing.T) {
+			actual, err := st.input.MarshalJSON()
+
+			require.NoError(t, err)
+			require.True(t, utf8.Valid(actual))
+			require.Equal(t, st.output, string(actual))
+		})
+	}
+}
diff --git a/pkg/types/bool.go b/pkg/types/bool.go
index 43302640..2b96c099 100644
--- a/pkg/types/bool.go
+++ b/pkg/types/bool.go
@@ -26,7 +26,7 @@ type Bool struct {
 // MarshalJSON implements the json.Marshaler interface.
 func (b Bool) MarshalJSON() ([]byte, error) {
 	if !b.Valid {
-		return nil, nil
+		return []byte("null"), nil
 	}
 
 	return internal.MarshalJSON(b.Bool)
diff --git a/pkg/types/bool_test.go b/pkg/types/bool_test.go
new file mode 100644
index 00000000..fe49588c
--- /dev/null
+++ b/pkg/types/bool_test.go
@@ -0,0 +1,30 @@
+package types
+
+import (
+	"fmt"
+	"github.com/stretchr/testify/require"
+	"testing"
+	"unicode/utf8"
+)
+
+func TestBool_MarshalJSON(t *testing.T) {
+	subtests := []struct {
+		input  Bool
+		output string
+	}{
+		{Bool{Bool: false, Valid: false}, `null`},
+		{Bool{Bool: false, Valid: true}, `false`},
+		{Bool{Bool: true, Valid: false}, `null`},
+		{Bool{Bool: true, Valid: true}, `true`},
+	}
+
+	for _, st := range subtests {
+		t.Run(fmt.Sprintf("Bool-%#v_Valid-%#v", st.input.Bool, st.input.Valid), func(t *testing.T) {
+			actual, err := st.input.MarshalJSON()
+
+			require.NoError(t, err)
+			require.True(t, utf8.Valid(actual))
+			require.Equal(t, st.output, string(actual))
+		})
+	}
+}
diff --git a/pkg/types/unix_milli.go b/pkg/types/unix_milli.go
index 203cdf6e..3f6f988f 100644
--- a/pkg/types/unix_milli.go
+++ b/pkg/types/unix_milli.go
@@ -24,7 +24,7 @@ func (t UnixMilli) Time() time.Time {
 // Marshals to milliseconds. Supports JSON null.
 func (t UnixMilli) MarshalJSON() ([]byte, error) {
 	if time.Time(t).IsZero() {
-		return nil, nil
+		return []byte("null"), nil
 	}
 
 	return []byte(strconv.FormatInt(time.Time(t).UnixMilli(), 10)), nil
diff --git a/pkg/types/unix_milli_test.go b/pkg/types/unix_milli_test.go
new file mode 100644
index 00000000..985fa2ac
--- /dev/null
+++ b/pkg/types/unix_milli_test.go
@@ -0,0 +1,30 @@
+package types
+
+import (
+	"github.com/stretchr/testify/require"
+	"testing"
+	"time"
+	"unicode/utf8"
+)
+
+func TestUnixMilli_MarshalJSON(t *testing.T) {
+	subtests := []struct {
+		name   string
+		input  UnixMilli
+		output string
+	}{
+		{"zero", UnixMilli{}, `null`},
+		{"epoch", UnixMilli(time.Unix(0, 0)), `0`},
+		{"nonzero", UnixMilli(time.Unix(1234567890, 62500000)), `1234567890062`},
+	}
+
+	for _, st := range subtests {
+		t.Run(st.name, func(t *testing.T) {
+			actual, err := st.input.MarshalJSON()
+
+			require.NoError(t, err)
+			require.True(t, utf8.Valid(actual))
+			require.Equal(t, st.output, string(actual))
+		})
+	}
+}