将参数传递给属性时如何防止自动转换？

Question

当我尝试将字符串（testString = "10"）参数传递给带有货币参数（ByVal newCash as Currency）的属性时，为什么它不会失败？我不希望这种自动转换。怎么预防呢？如何禁用它？

Model课程模块

Option Explicit

Private m_cash As Currency

Public Property Let Cash(ByVal newCash As Currency)
    m_cash = newCash
End Property

Test课程模块

Option Explicit

Public Sub Test()
    Dim modelObj as Model
    Dim testString as String

    Set modelObj = New Model
    testString = "10"

    modelObj.Cash = testString
End Sub