del

public/react/src/modules/courses/exercise/new/NullEditor.js

@@ -196,12 +196,14 @@ class NullEditor extends Component{
   }
   
   onAnswerChange = (index, itemIndex, val) => {
+    if (this.state.standard_answers[index]) {
     this.setState(
         (prevState) => ({ 
           standard_answers : update(prevState.standard_answers
             , {[index]: {$splice: [[itemIndex, 1, val]]}}),
         })
       )
+    }
   }
   addChildAnswer = (index) => {
     this.setState(