Fails to insert mention if no suggestion is specified.

[jameskraus]

If no suggestion is specified, this block of code fails to insert a suggestion.

          var selected = Math.abs(editor.state[_constants.SELECTED_MENTION_INDEX_KEY]); // selected = 0
          var text = suggestions[selected % suggestions.length || 0]; // text = undefined
          var at = (0, _utils.nearestAt)(state.endText.text, state.selection.startOffset);
          var mentionLength = state.selection.startOffset - at - 1;

          // Remove the current, incomplete text and replace it with the selected suggestion
          return state.transform().deleteBackward(mentionLength).insertText(text).removeMark('mention').insertText(' ').focus().apply(); // fails to insert `undefined` text

I get this error: Cannot read property 'length' of undefined

To reproduce, just enter an @mention that doesn't exist in the example and it will throw the error.

The two normal ways of handling this are to either create an ad-hoc mention or to not allow the user to create the mention at all. Considering the generality of this library, it seems appropriate to handle both cases?

[mxstbr]

Yep yep. This is very alpha, so lots of functionality like that is still missing 😉 Would appreciate PRs!