fix warning

client/src/cash/MakeMoneyMove.js

@@ -9,7 +9,7 @@ const MakeMoneyMove = (props) => {
     const [selectedFrom, setSelectedFrom] = useState("");
     const [selectedTo, setSelectedTo] = useState("");
     const [homiesCash, setHomiesCash] = useState([]);
-    const [amountToMove, setAmountToMove] = useState(null);
+    const [amountToMove, setAmountToMove] = useState('');
     const [moveDescription, setMoveDescription] = useState("");
     const [submitInProgress, setSubmitInProgress] = useState(false);