Add example for Nil value JSON unmarshaling

Introduced ExampleVariable_UnmarshalJSON to demonstrate unmarshaling of JSON with nil and non-nil fields. This includes handling for multiple custom types and provides a sample output. Added necessary imports and error handling for clarity.

niljson_test.go

@@ -7,6 +7,8 @@ package niljson
 import (
 	"bytes"
 	"encoding/json"
+	"fmt"
+	"os"
 	"testing"
 )
 
@@ -108,3 +110,48 @@ func TestVariable_UnmarshalJSON(t *testing.T) {
 		t.Errorf("expected string to be nil after reset")
 	}
 }
+
+func ExampleVariable_UnmarshalJSON() {
+	type JSONType struct {
+		Bool       NilBoolean   `json:"bool"`
+		ByteSlice  NilByteSlice `json:"bytes"`
+		Float32    NilFloat32   `json:"float32,omitempty"`
+		Float64    NilFloat64   `json:"float64"`
+		Int        NilInt       `json:"int"`
+		Int64      NilInt64     `json:"int64"`
+		NullString NilString    `json:"nilvalue,omitempty"`
+		String     NilString    `json:"string"`
+	}
+	data := []byte(`{
+ 		"bytes": "Ynl0ZXM=",
+		"bool": true,
+		"float32": null,
+		"float64":0,
+		"int": 123,
+		"int64": 12345678901234,
+		"nilvalue": null,
+		"string":"test"
+	}`)
+
+	var example JSONType
+	var output string
+	if err := json.Unmarshal(data, &example); err != nil {
+		fmt.Println("failed to unmarshal JSON:", err)
+		os.Exit(1)
+	}
+
+	if example.Bool.NotNil() {
+		output += fmt.Sprintf("Bool is: %t, ", example.Bool.Value())
+	}
+	if example.Float32.IsNil() {
+		output += "Float 32 is nil, "
+	}
+	if example.Float64.NotNil() {
+		output += fmt.Sprintf("Float 64 is: %f, ", example.Float64.Value())
+	}
+	if example.String.NotNil() {
+		output += fmt.Sprintf("String is: %s", example.String.Value())
+	}
+	fmt.Println(output)
+	// Output: Bool is: true, Float 32 is nil, Float 64 is: 0.000000, String is: test
+}