Why is flutter not calling the optionsbuilder in the autocomplete widget?

Question

Consider the following code

Widget returnAutoCompleteForTankLine(BuildContext context, MyAquariumManagerTanksModel tanksModel, TextEditingController textController, Tank? currentTank) {
    myPrint("in returnAutoCompleteForTankLine");
    return Autocomplete<String>(
      //initialValue: TextEditingValue(text: initialText),
      optionsBuilder: (TextEditingValue textEditingValue) {
        myPrint("in optionsbuilder");
        if (textEditingValue.text == '') {
          myPrint("in optionsbuilder, emptyee");
          return const Iterable<String>.empty();
        }
        myPrint("do we have tanklines, ${tanksModel.returnListOfTankLines()}");
        return tanksModel.returnListOfTankLines().where((String option) {
          return option.contains(textEditingValue.text.toLowerCase());
        });
      },
        fieldViewBuilder: (BuildContext context, TextEditingController textEditingController,
            FocusNode focusNode,
            VoidCallback onFieldSubmitted) {
          myPrint("in fieldViewBuilder");
          return TextField(
            controller: textController,
            focusNode: focusNode,
            onChanged: (String value) {
myPrint("do we come here?");
            },
          );
        }
    );
  }

The textfield works, but the code inside optionsBuilder never gets called. Why might this be?