Allow protected values to be empty

This makes them much more friendly to being put inside of STL containers, like maps.

src/jsc/jsc_protected.hpp

@@ -28,6 +28,7 @@ class Protected<JSGlobalContextRef> {
     JSGlobalContextRef m_context;
 
   public:
+    Protected() : m_context(nullptr) {}
     Protected(const Protected<JSGlobalContextRef> &other) : Protected(other.m_context) {}
     Protected(Protected<JSGlobalContextRef> &&other) : m_context(other.m_context) {
         other.m_context = nullptr;
@@ -43,6 +44,9 @@ class Protected<JSGlobalContextRef> {
     operator JSGlobalContextRef() const {
         return m_context;
     }
+    operator bool() const {
+        return m_context != nullptr;
+    }
 };
 
 template<>
@@ -51,6 +55,7 @@ class Protected<JSValueRef> {
     JSValueRef m_value;
 
   public:
+    Protected() {}
     Protected(const Protected<JSValueRef> &other) : Protected(other.m_context, other.m_value) {}
     Protected(Protected<JSValueRef> &&other) : m_context(other.m_context), m_value(other.m_value) {
         other.m_context = nullptr;
@@ -67,11 +72,15 @@ class Protected<JSValueRef> {
     operator JSValueRef() const {
         return m_value;
     }
+    operator bool() const {
+        return m_value != nullptr;
+    }
 };
 
 template<>
 class Protected<JSObjectRef> : public Protected<JSValueRef> {
   public:
+    Protected() : Protected<JSValueRef>() {}
     Protected(const Protected<JSObjectRef> &other) : Protected<JSValueRef>(other) {}
     Protected(Protected<JSObjectRef> &&other) : Protected<JSValueRef>(std::move(other)) {}
     Protected(JSContextRef ctx, JSObjectRef value) : Protected<JSValueRef>(ctx, value) {}

src/node/node_protected.hpp

@@ -29,11 +29,15 @@ class Protected {
     Nan::Persistent<MemberType, v8::CopyablePersistentTraits<MemberType>> m_value;
 
   public:
+    Protected() {}
     Protected(v8::Local<MemberType> value) : m_value(value) {}
 
     operator v8::Local<MemberType>() const {
         return Nan::New(m_value);
     }
+    operator bool() const {
+        return m_value.isEmpty();
+    }
     bool operator==(const v8::Local<MemberType> &other) const {
         return m_value == other;
     }
@@ -55,6 +59,7 @@ namespace js {
 template<>
 class Protected<node::Types::GlobalContext> : public node::Protected<v8::Context> {
   public:
+    Protected() : node::Protected<v8::Context>() {}
     Protected(v8::Local<v8::Context> ctx) : node::Protected<v8::Context>(ctx) {}
 
     operator v8::Isolate*() const {
@@ -65,18 +70,21 @@ class Protected<node::Types::GlobalContext> : public node::Protected<v8::Context
 template<>
 class Protected<node::Types::Value> : public node::Protected<v8::Value> {
   public:
+    Protected() : node::Protected<v8::Value>() {}
     Protected(v8::Isolate* isolate, v8::Local<v8::Value> value) : node::Protected<v8::Value>(value) {}
 };
 
 template<>
 class Protected<node::Types::Object> : public node::Protected<v8::Object> {
   public:
+    Protected() : node::Protected<v8::Object>() {}
     Protected(v8::Isolate* isolate, v8::Local<v8::Object> object) : node::Protected<v8::Object>(object) {}
 };
 
 template<>
 class Protected<node::Types::Function> : public node::Protected<v8::Function> {
   public:
+    Protected() : node::Protected<v8::Function>() {}
     Protected(v8::Isolate* isolate, v8::Local<v8::Function> object) : node::Protected<v8::Function>(object) {}
 };