fix single correct answer mode

editors/demo/src/HHMI/HHMI.js

@@ -170,7 +170,7 @@ const Hhmi = () => {
         value={content}
         readonly={readOnly}
         layout={HhmiLayout}
-        onChange={source => console.log(source)}
+        // onChange={source => console.log(source)}
       />
     </>
   );

wax-prosemirror-services/src/MatchingService/components/MatchingContainerComponent.js

@@ -139,12 +139,14 @@ export default ({ node, view, getPos }) => {
     const listener = event => {
       if (event.code === 'Enter') {
         event.preventDefault();
-        addOptionBtnRef.current.click();
+        if (addOptionBtnRef.current) addOptionBtnRef.current.click();
       }
     };
-    addOptionBtnRef.current.addEventListener('keydown', listener);
+    if (addOptionBtnRef.current)
+      addOptionBtnRef.current.addEventListener('keydown', listener);
     return () => {
-      addOptionBtnRef.current.removeEventListener('keydown', listener);
+      if (addOptionBtnRef.current)
+        addOptionBtnRef.current.removeEventListener('keydown', listener);
     };
   }, []);
 

wax-prosemirror-services/src/MultipleChoiceQuestionService/MultipleChoiceSingleCorrectQuestionService/components/SwitchComponent.js

@@ -69,7 +69,7 @@ const CustomSwitch = ({ node, getPos }) => {
         });
       } else if (
         element.type.name === 'multiple_choice_single_correct' &&
-        element.attrs.correct
+        element.attrs[key]
       ) {
         tr.setNodeMarkup(parentPosition + position + 1, undefined, {
           ...element.attrs,

wax-prosemirror-services/src/MultipleChoiceQuestionService/TrueFalseSingleCorrectQuestionService/components/SwitchComponent.js

@@ -69,7 +69,7 @@ const CustomSwitch = ({ node, getPos }) => {
         });
       } else if (
         element.type.name === 'true_false_single_correct' &&
-        element.attrs.correct
+        element.attrs[key]
       ) {
         tr.setNodeMarkup(parentPosition + position + 1, undefined, {
           ...element.attrs,