bindings: Add empty checks for toV8()

Source/bindings/templates/attributes.cpp

 {% from 'conversions.cpp' import declare_enum_validation_variable, v8_value_to_local_cpp_value %}
 
 
 {##############################################################################}
 {% macro attribute_getter(attribute, world_suffix) %}
 {% filter conditional(attribute.conditional_string) %}
 static void {{attribute.name}}AttributeGetter{{world_suffix}}(
 {%- if attribute.is_expose_js_accessors %}
 const v8::FunctionCallbackInfo<v8::Value>& info
 {%- else %}
@@ skipping 414 matching lines @@
     v8::Local<v8::Context> contextInPrivateScript = toV8Context(frame, DOMWrapperWorld::privateScriptIsolatedWorld());
     if (contextInPrivateScript.IsEmpty())
         return false;
     ScriptState* scriptState = ScriptState::from(contextInPrivateScript);
     ScriptState* scriptStateInUserScript = ScriptState::forMainWorld(frame);
     if (!scriptState->executionContext())
         return false;
 
     ScriptState::Scope scope(scriptState);
     v8::Local<v8::Value> holder = toV8(holderImpl, scriptState->context()->Global(), scriptState->isolate());
+    if (holder.IsEmpty())
+        return false;
 
     ExceptionState exceptionState(ExceptionState::GetterContext, "{{attribute.name}}", "{{cpp_class}}", scriptState->context()->Global(), scriptState->isolate());
     v8::Local<v8::Value> v8Value = PrivateScriptRunner::runDOMAttributeGetter(scriptState, scriptStateInUserScript, "{{cpp_class}}", "{{attribute.name}}", holder);
     if (v8Value.IsEmpty())
         return false;
     {{v8_value_to_local_cpp_value(attribute.private_script_v8_value_to_local_cpp_value) | indent}}
     RELEASE_ASSERT(!exceptionState.hadException());
     *result = cppValue;
     return true;
 }
@@ skipping 10 matching lines @@
     v8::Local<v8::Context> contextInPrivateScript = toV8Context(frame, DOMWrapperWorld::privateScriptIsolatedWorld());
     if (contextInPrivateScript.IsEmpty())
         return false;
     ScriptState* scriptState = ScriptState::from(contextInPrivateScript);
     ScriptState* scriptStateInUserScript = ScriptState::forMainWorld(frame);
     if (!scriptState->executionContext())
         return false;
 
     ScriptState::Scope scope(scriptState);
     v8::Local<v8::Value> holder = toV8(holderImpl, scriptState->context()->Global(), scriptState->isolate());
+    if (holder.IsEmpty())
+        return false;
 
     ExceptionState exceptionState(ExceptionState::SetterContext, "{{attribute.name}}", "{{cpp_class}}", scriptState->context()->Global(), scriptState->isolate());
     return PrivateScriptRunner::runDOMAttributeSetter(scriptState, scriptStateInUserScript, "{{cpp_class}}", "{{attribute.name}}", holder, {{attribute.private_script_cpp_value_to_v8_value}});
 }
 {% endmacro %}
 
 
 {##############################################################################}
 {% macro attribute_configuration(attribute) %}
 {% if attribute.constructor_type %}
@@ skipping 43 matching lines @@
        access_control,
        property_attribute,
        only_exposed_to_private_script,
    ] %}
 {% if not attribute.is_expose_js_accessors %}
 {% set attribute_configuration_list = attribute_configuration_list
                                     + [on_prototype] %}
 {% endif %}
 {{'{'}}{{attribute_configuration_list | join(', ')}}{{'}'}}
 {%- endmacro %}