Make default value of Text type usable (#25)

This makes a good use case where consumers write tests and just
want some default value instead of explicitly using NewText().

example_test.go

@@ -7,6 +7,12 @@ import (
 	"github.com/rsjethani/secret/v2"
 )
 
+func ExampleText() {
+	s := secret.Text{}
+	fmt.Println(s, s.Value())
+	//Output: *****
+}
+
 func ExampleNewText() {
 	s := secret.NewText("$ecre!")
 	fmt.Println(s, s.Value())

secret.go

@@ -12,8 +12,9 @@ import (
 // DefaultRedact is used by default if no other redact hint is given.
 const DefaultRedact string = "*****"
 
-// Text provides a way safely to store your secret value and a corresponding redact hint. By
-// default this redact hint is returned for operations like printing and serializing.
+// Text provides a way to safely store your secret value and a corresponding redact hint. This
+// redact hint what is used in operations like printing and serializing. The default
+// value of Text is usable.
 type Text struct {
 	// v is the actual secret values.
 	v *string
@@ -43,11 +44,17 @@ func NewText(s string, options ...func(*Text)) Text {
 // String implements the fmt.Stringer interface and returns only the redact hint. This prevents the
 // secret value from being printed to std*, logs etc.
 func (s Text) String() string {
+	if s.r == nil {
+		return DefaultRedact
+	}
 	return *s.r
 }
 
 // Value gives you access to the actual secret value stored inside Text.
 func (s Text) Value() string {
+	if s.v == nil {
+		return ""
+	}
 	return *s.v
 }
 

secret_test.go

@@ -5,7 +5,7 @@ import (
 	"testing"
 )
 
-func TestText_UnmarshalJSON_allocates_new_data_rather_than_overwiting_existing(t *testing.T) {
+func TestTextUnmarshalJSON_allocates_new_data_rather_than_overwriting_existing(t *testing.T) {
 	s1 := NewText("hello")
 
 	oldRedact := s1.r