estou com um problema, a calculadora não está executando o código, comecou a dar bugs no finalzinho do projeto. Dá isso no terminal:

[felipecastrosales]

════════ Exception caught by gesture ═══════════════════════════════════════════════════════════════
The following _TypeError was thrown while handling a gesture:
type 'List' is not a subtype of type 'String'

When the exception was thrown, this was the stack:
#0 Memory._setOperation (package:calculator/models/memory.dart:47:7)
#1 Memory.applyCommand (package:calculator/models/memory.dart:20:7)
#2 _CalculatorState._onPressed. (package:calculator/screens/calculator.dart:19:14)
#3 State.setState (package:flutter/src/widgets/framework.dart:1233:30)
#4 _CalculatorState._onPressed (package:calculator/screens/calculator.dart:18:5)
...
Handler: "onTap"
Recognizer: TapGestureRecognizer#71251
debugOwner: GestureDetector
state: possible
won arena
finalPosition: Offset(384.0, 756.8)
finalLocalPosition: Offset(59.5, 40.0)
button: 1
sent tap down
════════════════════════════════════════════════════════════════════════════════════════════════════

[felipecastrosales]

Consegui solucionar, dei um "flutter pub get" no terminal e a aplicação voltou ao normal. 😀👌